Design Guidelines
Size
Our maximum moulding size is approximately 500mm x 500mm x 200mm but should not exceed the maximum projected area shown in the example materials table. (Figure 1)
Maximum material volume approximately 70cc.
Project Area
Projected area is a two-dimensional area measurement of a three-dimensional object, by projecting its shape onto an arbitrary plane. You can think of the green projection as a shadow cast from the part with a light source directly over it.
Red surfaces = surface area
Green surfaces = projected area of this part
A taper applied to the faces of the part that prevents them from being parallel to the motion of the mould tool opening is described as draft. This keeps the part from being damaged due to scratching or scuffing as the part is ejected from the mould.
Recommended draft:
- 0.5 degrees as a minimum on all faces at 90 degrees to the moulds split line is strongly advised
- 2 degrees works very well in most situations
- 3 degrees is average for a shutoff (metal sliding on metal) and will depend on the depth of the shut
- 2 degrees is required for light texture
- 5 or more degrees is required for heavy texture
Undrafted Part
Drafted Part
Undercuts
Undercuts can be created using mechanical, hydraulic or air side actions or in some cases by piercing through the moulding faces.
Mechanical side action – moving at 90 degrees to the mould split line
Pierced through clip example
Ejector Pins
Please be advised that on the majority of parts there will be a witness of the ejection process. Parts with ejector pin marks are usually acceptable however if necessary they can be designed out of the part in some cases.
Ejector Pins
Pin Marks
Wall Thickness
With injection moulded parts, trying to maintain uniform wall thickness will help to prevent potential issues such as sink marks and warping.
As a general rule, ribs should be kept to a maximum thickness not exceeding two thirds of the adjoining walls.
Sink Marks
Keeping wall thickness and ribs within the limits above should prevent or at least keep sink marks to a minimum.
Bad Practice
Best Practice
Sharp Corners
Best practice with moulded parts is to avoid sharp corners. Sharp corners can be points of weakness and in some instances can increase tooling costs.
Bad Practice
Best Practice
Surface Finishes
A variety of surface finishes are available from a heavy spark to a polished surface. Speciality finishes can be applied as a secondary process if required.
- Non Cosmetic – Machining marks remain visible – usually for part internals (unseen) or functional
engineering mouldings - Semi cosmetic – Most machining mark removed – functional engineering mouldings.
- Cosmetic – Various sparked finish options
- Cosmetic – Polished
- Cosmetic – Various speciality finishes – textures
Sparked finish examples
Gates
Gates are the method used to fill the cavities.
Here is a selection of the most common:
Sub / tunnel gate
Directly onto the part – leaves a small discreet witness particularly on small parts. Generally speaking, the larger the component, the larger the witness will be.
Tab gate
Directly onto the part – leaves a witness where it is trimmed from the part. Tab gates can help to prevent sinking on larger sectioned parts, or to hold parts together such as a left hand and right hand side for assembly later.
Direct sprue gate
Directly onto the part leaving a snipped or machined witness. Can be in a hidden place (internal) or can be covered with a label.
Hot tip
Usually directly onto the part – saves material – leaves small mark on the part.
Tolerances
The tolerance table below is a guide only tolerances will vary from material to material. Critical dimensions
should be advised before mould making. Moulds can be left metal safe during the manufacturing process to
adjust the critical dimensions.
Dimension
1 to 20 (+/-mm) 21 to 100 (+/-mm) 101 to 160 (+/-mm)
Tolerance
0.075 – 0.125 0.100 to 0.170 0.200 – 0.375
Materials
Please find below a selection of our stock materials, please note there are many more available should none of these suit
your requirements, including flame retardant and filled versions of most materials.
Material |
Abbreviation |
Cost |
| Acrylonitrile / Butadiene / Styrene | ABS | Low |
| Acrylonitrile / Butadiene / Styrene / Polycarbonate | ABS/PC | Medium |
| Liquid Crystal Polymer | LCP | High |
| Polyamide / Acrylonitrile / Butadiene / Styrene | PA/PC | Medium |
| (Acetal) Polyoxymethylene | POM | Low |
| (Acrylic) Polymethylmethacrylate | PMMA | Low |
| High Impact Polystyrene | HIPS | Low |
| Low Density Polyethylene | LDPE | Low |
| (Nylon) Polyamide 6 | PA6 | Medium |
| (Nylon) Polyamide 66 | PA66 | Medium |
| (Nylon) Polyamide 12 | PA12 | High |
| Polycarbonate | PC | Medium |
| Polypropylene | PP | Low |
| Polyetherimide | PEI | High |
| Thermoplastic Elastomer TPE | TPE | Medium - High |
