Technology / Photochemical Machining (Pcm)

Photochemical Machining (Pcm)

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Indian Institute of Technology, Kanpur

PHOTOCHEMICAL MACHINING (PCM)

ME662 Advanced Machining Processes

Tarun Mankad Y4456

October 05, 2007

CONTENTS

INTRODUCTION 5

PROCESS OUTLINE 7

PROCESS COMPONENTS 8

PCM PRODUCTS 21

COST DRIVERS 27

ADVANTAGES OF PCM 28

CONCLUSION 29

REFERENCES 31

LIST OF ILLUSTRATIONS

Illustration 1: the current PCM process 7

Illustration 2: process flow-chart 9

Illustration 3: etch profile development with time 14

Illustration 4: existing Regeneration Systems 19

Illustration 5: problems with different regeneration methods 20

Illustration 6: disposal of waste elements 20

Illustration 7: idealized PCM process of the future 30

LIST OF TABLES

Table 1: different etching technologies and products 8

Table 2: PCM etchants 8

Table 3: cost drivers 21

INTRODUCTION

Definition:

Photo chemical machining is an engineering production technique for the manufacture of burr free and stress free flat metal components by selective chemical etching through a photographically produced mask.

Overview:

Photochemical machining (PCM) is one of the least well-known non-conventional machining processes. The technique is relatively modern and became established as a manufacturing process about fifty years ago.

PCM is also known as photoetching, photochemical milling, photomilling, photofabrication, photochemical etching and (in the USA) chemical blanking. The processing technology has been kept a closely-guarded secret within a small number of industrial companies but despite this, the sales of parts made by PCM at the end of the twentieth century was approximately US$ 6 billion. [1]

The PCM industry plays a valuable worldwide role in the production of metal precision parts and decorative items. Parts produced by PCM are typically thin, flat, and complex. These parts have applications in electronics, mechanical engineering, and the aerospace industry. The increasing popularity of industrial applications, together with greater competition, means that there is a need to understand the costs involved in PCM so that the right technology can be selected for manufacturing. [2]

PCM is generally categorized as a two dimensional manufacturing methodology, but the recent developments ,as well as, the work still being carried out in this direction, further widens the applicability of this process.

In order to compete with traditional manufacturing processes, PCM has undergone many process modifications in order to comply with a plethora of legislation and regulations aimed at protecting the environment. These modifications have greatly reduced the environmental impact of the process and the drive to reduce it further continues.

The environmental effects can be appreciable in view of the nature of the industry whereby various chemicals are used in the preparation and cleaning of metal surfaces, photographic processing of photo-tooling, coating and selective removal (development) of photo-resists, etching through apertures in the resist stencils and stripping of resist after etching.

Brief history of PCM:

Two developments within the space of forty years in photography laid the foundations for the photoresists we use today. In 1782 John Senebier of Geneva investigated the property of certain resins to become insoluble in turpentine after exposure to sunlight. Inspired by this, Joseph Nicephore Niepce resurrected an ancient Egyptian embalming technique that involved the use of what is now known as Syrian asphalt. This hardens after exposure to several hours of sunlight, into an acid resistant film. However, it took constant experimentation until this development was a success in 1822. The result was a resist that could be photo-polymerized in the exposed areas whereas the unexposed areas could be developed off in a solution of oil of lavender in turpentine. The age of photo etching had arrived. [6]

John Snellman may have been the first to produce flat metal components by photo chemical machining of shim stock that was too hard for punching. He innovated the use of cutting lines, or outlines, in the photoresist mask. This ensured even simultaneous etching of every component detail and also his use of tabs secured the parts into the parent metal sheet. He patented the process in 1944 where after it was increasingly used to manufacture shims, springs, stencils, screens and virtually any complex shape which for technical reasons could not be punched. Within ten years two American companies, the Texas Nameplate Company and the Chance-Vought Aircraft Corporation had taken a considerably refined Snellman’s process and renamed it Chemi-Cut. [6]

Although the first photoresist was developed in 1826, the start of the photochemical machining industry seemed to coincide with the development of the highly successful KPR family of photoresists marketed by Kodak in the mid-1950s. The first PCM companies were formed in North America and the UK but soon the technology was also being applied in mainland Europe and the Far East. Many of the job-shop (sub-contract) PCM companies were started by entrepreneurs as small spin-off companies intent on manufacturing piece-parts as a rapid and economic alternative to stamping. Some larger companies believed that the PCM process was so critical to their production that it was brought in-house to gain competitive advantage and preserve confidentiality. In the early days of commercial PCM, process technology was guarded jealously to the point that PCM was regarded as �Manufacturing’s Best Kept Secret’. [1] But with the advent of research and information, alongside the advantages, the process underwent fame and implementation.

PROCESS OUTLINE

In the multi-stage PCM process illustrated in Figure 1, the use of photo-resists enables fabrication of high resolution parts with complex, plan view geometry or with large arrays of variable aperture profiles in thin (< 2mm thick) flat metal sheet and thereby often bestows technical and economic advantages over:

• Traditional metal cutting techniques;

• Chemical milling used for lower resolution applications over larger areas;

• Other non-traditional machining techniques such as laser cutting, wire-EDM and stamping.

Figure 1: The current PCM process [1]

The method of material removal in PCM is based on the redox chemistry of etchant reduction effecting metal oxidation resulting in material dissolution with the formation of soluble byproducts that diffuse away from the reaction site. [1]

PCM is closely allied to several other techniques that utilize etching technology to produce parts. The differences in the techniques are shown in Table 1. It can be carried out on a very wide range of materials. Table 2 shows the main etchants used in PCM and some of the materials that can be etched in them. The main limitation of PCM is to be found in the characteristics of isotropic etching whereby the etchant will attack not only downwards into the metal but also sideways beneath the resist stencil layer. [1]

Table 1: Comparison of different etching technologies and products [1]

Table 2: PCM etchants [1]

PROCESS COMPONENTS

The PCM process tree comprises of the following levels or steps. In order to have the maximum efficiency with respect to cost, as well as, product aesthetics, the manufacturer needs to be careful at all these levels. A Flow chart that gives a further insight into the process tree has been shown in figure 2. The sub-parts (process components) and their details are as follows:

A. Work piece:

a) Metal: Most metals are suitable for the etching process. The method of production and the chemical composition both have a bearing on the rate of processing, the overall finished size, tolerance and the appearance of the etched edges. Some alloyed materials do cause particular problems to the process e.g. a high carbon content contaminates the etching chemicals unless filtered out at the processing stage, Silicon causes particular problems with both the etching rate and adhesion of the photoresist to the surface of the material .Precious metals can be successfully processed, but as special chemistry is required most

Figure 2: Detailed Process Flow-chart [6]

commercial etching companies do not process these metal types unless the volume is high enough to warrant the special conditions. Pre-plated materials are generally not processed as the etch rate of the plating metal will differ from the base metal. This could consequently cause tolerance problems and cut back the plated finish to unacceptable levels. Hence, plated components are etched and post plated.

The quality of the metal used for the process is always purchased as photoetch quality rather than standard commercial grade. The metal is cold rolled, high precision, especially in relation to the tolerance of the thickness of gauge. It also has a superior surface finish to standard commercial grade material. Surface finish varies according to metal type and condition. However the surface finish is always superior to standard commercial grade material stock.

Mechanical properties of the metal are unimportant to the photo etch process. Sheets need to be flat and free from surface contamination .Temper of the metal does not affect the etching process but may affect any post etch operations. The etching process acts on the material at a grain structure level, therefore metals with an even grain structure, yield better results than those without. Grain direction of the stock material is not critical. [6]

b) Glasses: The etching of glasses involves aqueous solutions of hydrofluoric acid (HF). This extremely aggressive etchant poses health and safety challenges. It should be noted that photosensitive glasses up to 2mm in thickness do not require a photoresist imaging process as the glasses themselves are UV light sensitive. The exposure dosage to UV light is required to be very high in comparison to that required for photo resist exposure.[1]

c) Polymers: The etching of polymers through polymeric photo resist stencils is a challenge in itself to determine etchant compatibility. However, poly(methylmethacrylate), polyimide and a few other plastics have been etched successfully to form devices such as flexible circuits and replacement lens haptics for cataract patients. [1]

B. Photo tooling:

In order to transfer the image of the required cutting lines onto the photoresist some form of masking has to be produced. This mask consists of a sheet of clear acetate with black lines where the photoresist is to be masked from the ultra violet source. As the metal is covered and etched on both faces 2 films are required, these films are known as a photo tool or P.R.E (punched register envelope). [6]

Technology now allows an image of the profile of the flat component to be transferred directly to the photographic film that is to be used as the photo tool by way of a light pen plotter. These plotters operate in exactly the same way as a pen and paper plotter except that photographic film is substituted for paper and light for ink. Upon receipt of a drawing a 2D CAD image is created, which may involve calculating bend allowances and inclusion of half etch detail where required. To allow for the etching process an etching compensation factor has to be added. This involves drawing the outside profile larger than the finished component size and holes and slots smaller. The amount of adjustment is directly proportional to the thickness of the metal being processed. [6]

Tools are always plotted so that in use the emulsion side of the film will be in direct contact with the photoresist; failure to adhere to this orientation will result in a diffused line. The life cycle of a photo tool is approximately 400 print cycles. For volume production runs it is often prudent to produce a negative master film from which a positive film can be quickly produced by the contact method. [6]

C. Metal preparation (Cleaning):

The selected metal has to be cleaned prior to having the photoresist applied .The cleaning operation is necessary to remove the oil, grease or any substance from the surface of the metal that would prevent good adhesion of the photoresist.

There are 2 methods of cleaning, mechanical and chemical. Mechanical cleaning usually involves some form of scrubbing in conjunction with a suitable mild degreasing solution. This method gives a good result but is not practical for very thin gauge metals, as it may lead to mechanical damage .Chemical cleaning is a mild pickling process. The sheets of raw material are suspended in a degreasing solution. After soaking for approximately 10 minutes the sheets are given a clean water rinse. [6]

D. Protective Coating (photoresist):

There are 4 types of photoresist - wet film positive, wet film negative, dry film positive and dry film negative. Negative film requires exposure to UV light to harden the film whereas positive film is softened when exposed to UV light. Thus, positive film is not appropriate for PCM.

a) Wet Film Negative:

This film is applied to the surface of the metal in liquid form.

Advantages: Wet film has lower cost than dry film and if applied correctly allows the use of finer etched lines. Better resolution can be achieved. The edges of the metal are coated including any slots or holes.

Disadvantages: The surface of the metal has to be cleaned to an extremely high standard. The work area where the resist is applied has to be dust free. Applying the resist is a dipping process and it is not easy to achieve a constant thickness of film, the viscosity of the liquid being critical. After draining the resist has to be baked, this is both costly and time consuming. The resist has to be removed or stripped from the finished components with a solvent based cleaner, which does cause environmental issues, especially the control of noxious solvent fumes. [6]

b) Dry Film Negative:

The resist is protected by a polymer film which does not have to be removed until the sheet is developed. This polymer film gives protection to the resist in its soft, pre-exposed state. The film is applied to the metal sheets by a combination of heat and pressure by way of heated rollers.

Advantages: The application of the film is not so critical to dust; If the sheets are laminated whilst still wet from the cleaning rinse, the laminating rollers remove the water along with any dust on the metal surface. A constant thickness of film is assured. The polymer coating on the film helps protect the resist from damage during printing. Dry film laminating is a faster process than wet. If an aqueous based resist is used then the stripping process requires no solvent-based chemicals, and it can be stripped with a caustic soda solution.

Disadvantages: The material costs are much higher than with wet film. It is not possible to coat the edges of holes; slots or the metal sheet with resist. A range of widths and thicknesses has to be stocked to allow efficient use of materials. [6]

E. Laminating:

Laminating (the application of the photoresist) is carried out immediately after the metal has been cleaned. The process is dependent upon the type of photoresist being used.

For wet film resist the metal sheets are dipped into the liquid resist and allowed to drain until an even thickness of coating is achieved. The coated sheets are then baked in an oven to cure the film prior to printing and developing.

For dry film resist the sheets can be fed through the laminating rollers whilst they are still wet. The polymer film is left on the surface of the photoresist until the printing operation has been undertaken unless the sheets are to be double laminated. Both types of film now have to be protected from uncontrolled ultra violet light until the developing process has been undertaken. [6]

F. Image Creation (Printing):

The printing of the metal sheet is carried out by using a punch registered envelope which consists of 2 photographic films and an ultra violet light source. The object of the printing and developing process is to produce sheets that have cut lines i.e. bare metal areas on both faces where the etchant is required to act. Where the metal is to be unaffected by the process it remains covered in photoresist film. Once the phototools are in contact with the surface of the photoresist the whole assembly is exposed to an ultra violet light source. The exposure time is dependent upon the thickness of the masking lines present on the phototool. [6]

G. Image Creation (Developing):

Developing is the term used for the chemical removal of the unplasticised areas of the photoresist. The printed sheets are passed through the developing machine on a conveyor, where the unexposed areas of resist are removed with a sodium carbonate based solution. It is during the developing stage the bare metal cutting lines are produced. The developing operation is the final task before the sheets are subjected to the photo chemical machining process. Once developed the prepared sheets are no longer sensitive to ultra violet light. [6]

H. Etching:

a) Chemistry: The majority of photo chemical machining is carried out with aqueous solutions of ferric chloride. It is inexpensive, readily available, versatile, in that it attacks the majority of commonly used engineering metals and alloys, and it has a high capacity for dissolving those metals. Environmentally it is attractive as it is of low toxicity and relatively easy to filter, replenish and recycle. Also it is used extensively in water treatment processes. Ferric nitrate is used for the etching of non-standard materials such as Molybdenum and Silver.

Regular monitoring of the PCM process on the go is essential, as the properties of the etchant chemistry will alter constantly as they react to the elements transferred into solution from the materials etched. The elements added to the chemistry can increase or decrease the effective strength of the etchant. A consistent etch rate is important for production rate, etch quality and dimensional stability of the processed components. [6]

b) Rate of Etch/ dimension control: The depth of cut achieved during each pass through the etching machines depends on the length of the machine, the speed of the conveyers and the pressure and the strength of the etchant. [6]

Figure 3: Etch profile development (from top to bottom) as etching time increases. [1]

c) Etch Factor:

The ratio of etch depth to undercut is called etch factor and is determined by the process chemistry and the spray pressure and direction of its application. The differential etch rates at the floor and sides of the spray etch cavity are responsible for the characteristic profile of the finished edge. The profile develops as if an ellipse of increasing size were sinking into the metal surface. As etchant is applied under pressure then the point that receives the greatest impact of that pressure will etch quicker. This is always intended to be the base of the cut; therefore the cut will travel down (and up) through the material quicker than along the horizontal. The most productive etch rate is achieved when the etchant is sprayed perpendicular to the workpiece. This ensures that as the cut moves through the workpiece the main pressure is directed to the base of the cut, therefore only attacking the side walls by diffusion. [6]

Figure 4: Etchant Diffusion [6]

This is the result of simultaneous etching from both sides leaving a witness at the point of breakthrough. As the etching proceeds the bicuspid edge retreats at a decreasing rate. The nearer to the horizontal the surface the faster it etches, therefore the protruding cusp is reduced faster than the nearly vertical sidewalls. The rate of etch slows as the edge profile becomes vertical. Consequently if the product comes to size midway through a machine pass it will not be over etched and therefore undersize by the end of the pass. [6]

d) Etchant Variables/Parameters:

To maintain a constant rate of etching and hence control of part dimensions the etchant composition would be constant. Unfortunately, in the real world, the etchant composition changes continuously. As an n-valent metal (M) is dissolved into solution, etchant is consumed and the by-products of ferrous chloride (FeCl2) and metal chlorides (MCln) are generated. [4]

Thus, for quality control (QC) of PCM, this creates a specific demand for data relating to the composition of the etchant as it changes. There are various parameters that are typically measured in commercial enterprises in order to assess the quality of the etchant. These include:

п‚џ Лљ BaumГ© (or specific gravity);

п‚џ Temperature;

п‚џ free acid (HCl content);

 oxidation–reduction potential (ORP);

п‚џ Dissolved metal content.

The measurement of ORP gives an indication of the activity of the etchant. High values of ORP indicate an efficient etchant whilst low values of ORP indicate a slow and inefficient etchant. Ideally, we would like to maintain ORP at a high constant value for a constant etch rate of metal.

Variations in any of the above can affect amongst other things, the rate of etch (with a resultant change in etched dimensions) and surface finish. Theoretically, by monitoring variations in the parameters, it should be possible to predict the behaviour of the etchant. This in turn would assist in deciding whether to continue etching or replace the etchant or when to regenerate it. [4]

Interdependent variation in parameters:

п‚џ Conductivity decreases with ЛљBaumГ© (as the specific gravity increases, mobility of the ions decrease [4]

п‚џ Conductivity increases with increasing free acid content; Figure 9 [4]

п‚џ Conductivity of the etchant increases with temperature. Figure 6 [4]

п‚џ

where E = ORP (V), E0 formal is the electrode potential in concentrated solutions (V), R the gas constant (8.31 J/mol K), T the absolute temperature (K), n the number of electrons changed in the redox reaction, F the Faraday constant (9.6485 Г— 104 C/mol), [Fe3+] the concentration of ferric ions (M) and [Fe2+] is the concentration of ferrous ions (M). As can be seen from the equation, ORP increases with an increase of temperature. Figure 7 [4]

п‚џ

Higher the temperature, lower the pH value. [4]

п‚џ Conductivity is inversely related to pH. Figure 8 [4]

п‚џ pH decreases with increasing [H+]. [4]

Fig 9: Conductivity of H+ vs. free acid content for Analar grade 45 в—¦Be FeCl3 (at 20 в—¦C). [4]

Thus, during the process, in order to attain a better performance from the etchant, constant monitoring of these etchant parameters is needed. As etching proceeds:

п‚џ heat will be liberated from the exothermic reaction and care must be taken to cool the etchant;

п‚џ the ORP will decrease due to the consumption of ferric ions and the increase in ferrous ions;

п‚џ free acid level will fall as the HCl in solution will be driven off at the higher operating temperatures.[4]

As etching proceeds therefore:

п‚џ BaumГ© (or specific gravity) will rise as more material is dissolved in the same volume of etchant;

п‚џ ORP will fall;

п‚џ pH will rise (become more positive);

п‚џ conductivity will fall due to

1. A rise in ЛљBaumГ© ;

2. A fall in free acid.

I. Removal of Photoresist (Stripping) & Environmental Considerations:

Photoresist can only be removed by chemical means to avoid damage to the etched components. Different chemicals are utilized to strip different resist formulations. However the photoresist in most common usage is aqueous dry film that can be effectively stripped using a mild caustic soda solution. Alternatively if the components are loose, then they will be hand stripped in mesh baskets in dip tanks. Once stripped, the components are dimensionally inspected and ready for any appropriate secondary operations, such as plating forming, machining, assembly etc. [6]

As PCM involves use of various chemicals at different stages of operation (cleaning, masking, etching etc.), the environmental effects from the wastes generated are appreciable. The most common etchant is an aqueous solution of ferric chloride. The spent etchant and its rinse water contain heavy metal ions such as nickel and chromium which are hazardous to environment and most difficult to render harmless. [3]

Methods that can be employed to reduce the overall consumption of ferric Chloride include prolonging the life of the etchant by increasing the degree of �exhaustion’ of etchant before disposal, with the drawback of reduced etch rate, and regenerating the spent etchant by in situ oxidation, thus maintaining a constant etch rate. [3]

The existing regenerative processes have been shown in figure10. The different methods and their respective outputs, along with the environmental issues related, have been tabulated in figure11. Finally, the disposal routes have been shown in figure12

Figure 10: Existing Regeneration Systems [3]

Figure 11: problems with different regeneration methods [3]

Figure 12: Disposal of waste elements [3]

The �greening’ of PCM will encourage more use of:

• Aqueous, natural product and electrophoretic resists;

• LASER direct imaging (LDI) of photoresists, thereby eliminating photographic processing;

• High resolution ink jet printing of resists, again eliminating photographic processing;

• Environment-friendly etchant regeneration (the extraction of dissolved metal ions with simultaneous conversion of the waste ferrous chloride byproduct back to ferric chloride etchant) and

• Monitoring and automation of the etching process to increase process efficiency. [1]

PCM PRODUCTS

a) Micro engineering products: PCM is now also used to fabricate components used in Microsystems technology (MST) / micro-electro-mechanical systems (MEMS), medical diagnostic equipment and biomedical engineering applications such as body implants. In the past decade there has been an interesting rise in the number of non-silicon MEMS applications. For instance, miniature wings for micro air vehicles (MAVs) have been constructed from etched Ti-6Al-4V alloy struts covered with Parylene membranes. [1]

b) Aesthetic products: In addition to the above, PCM can provide parts with intrinsic aesthetic value and is much used for the production of jewelry, signage, commemorative plaques and Christmas decorations. Very often, the etching process is combined with electroplating, anodizing, lacquering and/or painting processes to give additional color and contrast. Whilst dimensional specifications might not be critical for decorative parts, visual appearance absolutely is. [1]

One of the important aspects of PCM is that the cross-sectional profile of etched features can be varied through the material thickness. Use of this attribute is made particularly in the fabrication of TV shadow aperture masks and hybrid circuit pack lids. [1]

PCM has provided a major, rapid-response service to supply components to the microelectronics, electrical and mechanical engineering industries over the past fifty years. The demand has been for relatively thin (< 2mm thick), complex, precision parts at an economic price. Prime examples are TV shadow aperture masks integrated circuit lead frames , disk drive suspension head assemblies), fine screens, sieves and meshes, shims, washers, laminations, optical shutters and light chopper discs, scales, filters, EMC/RFI enclosures (folded boxes), cutting blades and hybrid circuit pack lids. More recent developments include the use of etched gaskets in mobile telephones’ stainless steel bearing foil utilized in the reading head of a 30-60 Gb memory capacity streamer. [1]

Using the diffusion-bonding process printed circuit heat exchangers (PCHEs) have been used to construct heat exchangers over 109 tons in weight. As the width of an etching machine is the limiting factor, it has been known to convert two old identical etching machines into a �double width’ machine to overcome the limitation. [1]

More complex products such as oval blood pressure sensor bodies (2.275 x 0.67 x 0.1mm) containing three holes and a surface-etched drainage channel connected into a half-etch recess .The resolution of etched parts depends on material thickness and thus the most intricate parts are fabricated from the thinnest materials. Such materials present handling challenges as thin foils can be easily bent and damaged during processing. [1]

Figure 13: Lens haptics etched from 0.125 mm thick Kaptonв„ў polyimide film (Courtesy of Tech-Etch Inc., MA, USA). [1]

Figure 14: Etched suspension head assemblies (Courtesy of Hutchinson Technology Inc., MN, USA). [1]

Figure 15: Etched mobile telephone gasket (Courtesy of Savcor, Copenhagen, Denmark). [1]

Figure 16: 60 mm wide integrated circuit leadframes (Courtesy of Microponent Ltd, Birmingham, UK). [1]

Figure 17: Chemically engraved Cartier watch movements for a 25mm diameter wristwatch (Courtesy of CMTRickenbach, La Chaux-de-Fonds, Switzerland). [1]

Figure 18: 100 mm diameter, laminated stainless steel micro combustor/reactor components after final machining(from left to right) reactor, combustor and top plate (Courtesy of Pacific Northwest National Laboratory, USA). [1]

Figure 19: SEM of 0.5 x 0.5 mm Kovar packing carriers showing the characteristic profile (Courtesy of Tecan Ltd., Weymouth, UK). [1]

More PCM Products (Courtesy Internet)

COST DRIVERS:

Table lists up the different factors at various stages of the PCM operation, and their inter-relationship. It clearly mentions the cost drivers at different levels.

Table 3: Cost Drivers for PCM process [2]

ADVANTAGES OF PHOTO CHEMICAL MACHINING:

• Multi level depth etching;

• Low cost tooling of the process;

• Virtually, applicable for every metal type;

• Stress and burr free manufacture;

• No additional costs for complex shapes;

• Interfaces easily with other manufacturing techniques;

• No impact on component material properties;

• & Economic manufacturing costs. [6]

Comparisons of PCM with stamping

In comparing the production economics of these two processes, the relative costs of the �tools’ are important factors. A phototool is relatively cheap to produce using a photographic process and contrasts with the production of a more expensive �hard’ stamping tool requiring machining by a craftsman. However, the running costs of PCM are more expensive than those of stamping. Stamping becomes economically viable when high volumes of product are to be produced. [1]

Comparisons of PCM with stamping, wire-EDM and LASER machining

PCM turns out to be the most economic process for parts of high complexity. This is due to the fact that the etching process is not sequential and therefore it becomes possible to etch, say, 3 million holes in the same time that it takes to etch one hole. [1]

CONCLUSIONS

There appear to be many opportunities for PCM in the future. The technique has the following attributes that should ensure a prosperous future.

• With its ability for rapid production (e.g. prototype part production within 24 hours), it is compatible with agile manufacturing.

• Miniaturization and part complexity favor PCM for economic part production. As the etching process

is not sequential, it allows the etching of millions of high resolution apertures or features in a single operation.

• As product sophistication increases, a trend to the use of more exotic materials in products has been detected. These materials are often difficult-to-machine conventionally, often corrosion-resistant, usually costly to purchase and consequently may require a hybrid electrochemical/photochemical machining process to attain an acceptable rate of metal dissolution. Fine arts students and practitioners are beginning to discover the benefits of PCM. The technique is now used in architectural art and model-making, sculptures, jewelry, clock- and watch-making, signage, recognition awards and luxury decorative goods. [1]

•The main reason for not regenerating was a lack of technical knowledge in understanding the basic know-how of regeneration systems. Hence, if technical training is given to the companies concerned, the proportion of companies using regeneration could be increased. [3]

• The PCM industry continues to lower the environmental impact of its activities and an idealized process is kept as a benchmark (figure 20).Attempts are being made to remove all the organic solvents from metal preparation, photoresist coating, development and stripping and it is conceivable that photographic processing can also be eliminated. [5]

• Three Dimensional PCM – the development of a generic technique that dispenses with photo tools will solve the problem of imaging on complex surfaces. However, whilst this technique may become technically feasible (LASER guided 3-D PCM research is new on the list), economic considerations will restrict its usage and the use of conventional photo tooling will continue on planar, cylindrical, conical and spherical surfaces for the foreseeable future. [7]

• The best estimate for PCM sales at the end of the 20th century appears to be approximately US $5.8 billion. The maximum of US $8.3 billion and minimum of US $3.9 billion (giving an average of US $6.1 billion) indicate that the best estimate may be somewhat conservative and lower than the true figure. [1]

Figure 20: An idealized PCM process of the future [5]

REFERENCES

[1] Allen, D.M., 2004, Photochemical Machining: from �manufacturing’s best kept secret’ to a $6 billion per annum, rapid manufacturing process, Annals of the CIRP, 53/2.

[2] Roy R., Allen D.M. and Zamora O., 2004, Cost of photochemical machining, Journal of Materials Processing Technology, 149, 460-465.

[3] Allen, D.M. and Ler, L.T., 1999, Increasing utilization efficiency of ferric chloride etchant in industrial photochemical machining, J. Environmental Monitoring, 1, 103-108.

[4] Allen, D.M. and Almond H.J.A., 2004, Characterization of aqueous ferric chloride etchants used in industrial photochemical machining, Journal of Materials Processing Technology, 149, 238-245.

[5] Allen, D.M., 1993, Progress towards clean technology for photochemical machining, Annals of the CIRP, 42/1,197-200.

[6] PCM fundamentals, www.qualitetch.co.uk/documents/white_paper.

[7] Allen, D.M., 1987, Three-dimensional photochemical machining, Annals of the CIRP, 36/1, 91-94.

PHOTO CHEMICAL MACHINING

ME662

Rahul Choudhary Y4317

REFERRED MATERIAL:

[1] Allen, D.M., 2004, Photochemical Machining: from �manufacturing’s best kept secret’ to a $6 billion per annum, rapid manufacturing process, Annals of the CIRP, 53/2.

[2] Roy R., Allen D.M. and Zamora O., 2004, Cost of photochemical machining, Journal of Materials Processing Technology, 149, 460-465.

[3] Allen, D.M. and Ler, L.T., 1999, Increasing utilization efficiency of ferric chloride etchant in industrial photochemical machining, J. Environmental Monitoring, 1, 103-108.

[4] Allen, D.M. and Almond H.J.A., 2004, Characterization of aqueous ferric chloride etchants used in industrial photochemical machining, Journal of Materials Processing Technology, 149, 238-245.

[5] Allen, D.M., 1993, Progress towards clean technology for photochemical machining, Annals of the CIRP, 42/1,197-200.

[6] Allen, D.M., 1987, Three-dimensional photochemical machining, Annals of the CIRP, 36/1, 91-94.



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