Making Sole Moulds -1: Introduction
Moulds are hollow container into which a liquid or liquefied hot material is poured to set in to a desired shape. The mould is in general is the reverse of the required shape. Moulds are usually made for specific applications with their own unique features. Mould makers are the custom builders who design and manufacture these products for particular application.
Mould making requires expensive & precision equipment and also considerable skill. Each pair of sole mould (left & right) cost several thousand of rupees and every size requires separate mould.
A typical mould making workshop will have 10 to 50 highly trained people expertise in various fields like materials (both metallurgy and plastics), pneumatics, hydraulics, mould makers, EDM operators, CNC operators, Engravers and many other categories of skilled workers.
Most of the footwear soling materials are prepared by injection process, but in some cases like in DVP, EVA, PU sole are made by different process. The Footwear sole molds are made from metal, usually from steel, aluminum, copper and sometimes with Gun metal.
Injection molding is a manufacturing technique for making parts from plastic material. Molten plastic is injected at high pressure into a mould. Injection molding is very widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars.
In olden days and even sometimes now also, sole moulds are manufactured using conventional machines like PANTOGRAPHS, PLANER, FLEXIBLE GRINDERS etc. and quality of moulds depends on the skills of worker. With increasing use of technology such as CAD/CAM, Rapid Prototyping, Casting process, CNC milling, CNC spark erosion (EDM) techniques, digital design data can be translated directly into prototype and moulds are produced by casting process with in a period of 3 to 4 days.
Using a CAD software, Designer can create 3 Dimensional Sole model either from drawings and or from scan data of the sole (called Reverse Engineering).
Computer aided design was introduced in the shoe industry in 1970’s. Initially it was used primarily for footwear pattern grading. It enables the designers to perform complex grading relatively eas
ily and quickly. CAD systems today have been developed with a much wider range of functions. It automates the routine procedures, increasing speed and consistency whilst reducing the possibility of mistakes.
Using CAD systems, one can design the 3-Dimensional sole model and mould later in computer and NC programmes can be created for sole moulds and later this data can be send to CNC machine. A CAD system will includes the facilities to design and modify sole design and to create NC programes. Some softwares having the facilities to simulate the material flow in the mould. Even some computer software will assist in mould design also some mould flow type packages like Varicut, Moldflow will show how the molten material flow in and ar
ound the mould during filling or injection. Such software will help in designing effective tread pattern designs where air is likely to trap in the final moulding.
Latest trend of Rapid prototyping (where you create/manufacture a sole model before you go for actual production) allows so
Benefits of CAD/CAM in the mould manufacturing are:
- Total modeling for generation of design concepts and variations.
- Reverse engineering from existing models or parts.
- Easy to modify design.
- Completely accurate designs regardless of complexity.
- Rapid generation of moulds from product designs and Grading of sole models
- Easy to creates manufacturing documentation.
- Creates NC tool paths
- Creates NC tool paths
3D CAD/CAM is the core technology for present sole mould manufacturers in the footwear industry. With CAD/CAM software, footwear sole manufacturers can reduce their time to market dramatically and so increase market share and profitability. In addition, the flexibility of the software can overcome restrictions of the designer’s creativity impos ed by traditional methods and sole mould makers are able to strengthen their capabilities of mould design and production techniques to meet the market demands by shortening product life cycle, quality improvement and handling versatile pattern design. This helps especially sports shoe producers to manufacture products rapidly and to introduce them early than their competitors.
Even after introduction of CAD still some operations like assembling, etching etc to be done manually. You cannot avoid manual intervention completely.
Contributor: A.V.Suresh, Footwear CAD Engineer