![]() When trimming on a 5-axis router the parts are usually held on a jig locating the moulding on the controlled face.If 2 parts are to fit together, the only way of ensuring the fit is to have 2 controlled faces meeting each other.The controlled surface is always the tool side of the part. It is important to consider the controlled surfaces. Tip! Two 10mm high ribs must have 10mm spacing between them as minimum. Avoid areas which are narrow and tall as parts will thin too much on forming and split on ejection and cause webbing.The taller the part the thicker the material required. Material starting thickness required 3 x 2 = 6mm Total surface area of the part A is divided by footprint of the part B. The draw ratio can be calculated but this is only to be used as a guide as every shape will react slightly differently on the flow and distribution of the material. It will then stretch to cover the mould and as the sheet stretches, it thins out. The sheet is heated and formed over or into a mould. The 3-dimensional part has a surface area that needs to be covered by a flat two-dimensional sheet. The draw ratio is important to understanding the process. Tip! Avoid tall narrow areas which cause parts not to release from the mould. The taller the part the thinner the material required to cover the whole part. Height of sand castle compared to diameter). 3) Draw Ratio/Required material thicknessÄraw ratio refers to the height of the part to be formed compared to the footprint of the part (back to the sand castle i.e. Tip! As the plastic cools it will shrink onto a male tool but away from a female tool hence the less draft required on female tools. Allow as much draft as the design will accommodate.This will show where webs will develop! Sharp corners are to be avoided as this will hinder the flow of material and maximise the chance of webbing. Take a cigarette packet and try forcing a sheet of paper over it. showing how the corners will pleat/web during forming. This will give you a good idea of where the problems will be when forming, i.e. When you start to design your part imagine that you are draping a cloth or a sheet of paper over the part. Guidelines for Designing Parts 1) Material Flow and Webbing More detail can be achieved with this process, but tooling is more complicated and expensive. The Pressure Forming ProcessĪs above but with the addition of applying compressed air to the outer surface of the plastic sheet. The sheets are heated and then sucked down by applying a vacuum to the underside of the mould, atmospheric air pressure then forces the heated plastic to adopt the shape of the mould. This is the process of moulding extruded plastic sheets heated to a pre-determined temperature. ![]()
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