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PNP Plastics

Paul Norman Plastics

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Product Design

Turning your vision into reality

Tooling

Precision tooling backed by 100 years British toolmaking experience

Plastic Moulded Components

Bespoke plastic injection moulded components and assemblies

Secondary Operations

Value added services

Design Guidelines

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.

project-area1
project-area2

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

undrafted-part

Drafted 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.

undercuts

Mechanical side action – moving at 90 degrees to the mould split line

undercuts-2

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

ejector-pins1

Pin Marks

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.

wall-thickness

Sink Marks

Keeping wall thickness and ribs within the limits above should prevent or at least keep sink marks to a minimum.

Bad Practice

sink-mark

Best 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

sharp-corner

Best Practice

radius-corner

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

sparked-finish
sparked-finish-2

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.

sub-gate

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.

tab-gate

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.

sprue-gate

Hot tip

Usually directly onto the part – saves material – leaves small mark on the part.

hot-tip

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