Photochemical Machining (Pcm)

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