Making Sole Moulds -4 : Process of making Sole Mould (by CAD/CAM )
Process of making Sole Mould (by CAD/CAM )
A mould generally contains different parts depending on
- Sole design (Single color, multi color)
- Sole material
- Machine type etc.
In general all the moulds contains two parts i.e Lower part (cavity) and upper part (Core). Some times it requires to split the core or cavity into multiple parts depending on the design. These are called inserts of core or cavity respectively.
The manufacturing of a sole mould can be explained by taking a simple example. Let us assume that we have to prepare a mould for the sole shown in the picture.
The following check list can help the sole mould designer before designing the sole design/mould
- Study carefully your existing documentation/drawings about the sole to be designed.
- Check information about molding machine etc
- Consider the shrinkage allowances both for sole and sole mould material.
- Determine the location of brand names, sizes and logos in sole. ((Ex. When we mirror the sole design to opposite foot, the logo will also mirror. But in real caes the logo should not be mirrored)
- Define the objects which do not vary with sizes.
- Select the suitable parting surface.
- Determine the number of inserts required.
- Select material for molding parts, inserts particularly in case of EDM
- Choose appropriate gate position on the mould.
- Select appropriate guide pillars and bushes.
- Elimination of air entrapment by providing air vents and their location.
- Determine the way of ejection, location and dimensions of ejector rod.
- Determine the location of pressure end switch.
- Determine the process of assembling.
- Determine the position of flash channels for compression moulds.
- Determine the type of locking system.
- Determine the material removing process for making mould and inserts.
- Determine the methods for surface finish/ texture producing etc.,
- Determine the direct cooling and heating of the mold if necessary
The first thing while designing the Mould is to decide the parting surface/parting line, to prepare core and cavity. Selection of parting line should be done by careful studying the sole design. While selecting the parting line we have to consider the following
• Ejection /removal of sole should be easy.
• Possibility of machining the core and cavity
• Reduce the machining time.
Once the parting line is selected the next step is to prepare the mould core and cavity. As already mentioned machining the complete model with CNC machine is not economical. In general combination of manual and CNC methods are used to complete the mould. Ex locating pins, runners etc., are prepared manually after finishing core and cavity. The core and cavity for above sole will looks below.
But if you see the core part, machining of the same is very difficult and consumes times particular at the end of the sole lip area where we need very sharp at the base. Even the extruded pins on the core, which are difficult to machine. In order to save time and to get sharp corners, core is prepared in two parts i.e core and core insert. Later both are fitted to make one.
Similar process is used in many cases, where you need to produce sharp corners. Even in cavity also a separate inserts are prepared and inserted, particularly in heel areas where sharp corner is impossible to machine. Another method to get sharp corners is use of EDM process. So the Sole designer/ mould maker have to decide the method that suits best .
The core insert has pins. These pins will reduce the weight of the sole. To simplify the process, the core is prepared without pins and later Aluminium rods are inserted in the core insert. To do this holes are drilled in the insert and Aluminium pins are snug fitted into them.
Once the core cavities are prepared the next step is to assemble and finish the moulds. After milling the mould generally the mould contain tool path marks, scratches etc. These have to be removed first. All the surfaces of the mould should be free from scratch marks. The mould cavity can be polished smooth to impart a gloss to the sole, or it can be sand blasted to give mat finish.
Written by : A.V.Suresh, Footwear CAD Engineer