Engineering Resources

The main function of this section is to assist product designers or engineers to quick design easy-manufactured parts, which meet function requirements as well as attract end users. The topics discussed in this section are from Leadwin knowledge base, which are accumulated from 30 years practices. We will randomly discuss the topic based on reader’s request.. The information in this section is for general purposes. It might be needed to adjust according to your specific case.
If you have something you want to know and do not find in this section, you are welcome to write to us. We are pleased to assist you to find solutions.

  • How to define the draft angle for a plastic part?

Plastic part is formed by two cores (A side and B side). At A side and B side core match area it will form a parting line. This parting line will leave a mark and small flash on part. To avoid parting line causing cosmetic problems, designers will try to put parting line on edge. 

The diagram on right shows α draft angle as B side draft angle and β draft angle as A side draft angle. The purpose of draft angle is to avoid scratch on steel mold and plastic part when mold opening. If the draft is too small, when mold opens; it causes scratch on plastic part. Sometime, the part is stuck in A side which makes ejection system useless. Therefore, people prefer to have larger draft angle on A side than on B side. If the draft angle on B side is too small, the ejector pins might push too hard which make pin push marks as well as scratch on part surface.

The bigger draft angle will help part ejected from mold. But too big draft angle will make part distortion and with funny shape. In addition, it is hard to assembly two parts together with non-consistent draft angle. Certainly, the designer wants to reduce draft angle too.

The degree of draft angle depends on the roughness of plastic part. The rougher surface; the larger draft angle. For example, a plastic part with MT11020® texture requires 3 degree of draft angle. However this is a general recommendation. The appropriate draft angle depends on the property of steel, the property of resin, the depth of wall…and so on. There are many cases that product designers can not afford to give enough draft angle because of cosmetic concern or difficulty on assembly. It will cause low yield rate, shorter mold life and high maintenance cost. When molders need to use mold release to produce a part, it is a signal that part does not have enough draft angle.

The product designer knows the impact of draft angle. But it is hard for product designer to design a product with draft angle at the first place because the prototype will be modified many times before final approval. To change draft angle is not an easy job. Therefore product designers will design the product without draft angle. Then the product designer will add draft angle based on DFM analysis or after the first prototype satisfies cosmetic and functional requirements. It is a little bit late but it is a common practice. An experienced product designer will start his design with draft angle in mind. This can avoid the trade-off between appearance and manufacturability.

For questions on draft angle, please email us.

  • How to define radius and acute angle?

When product designer designs his product, he will not draw edges with radius unless it is necessary. The product designer will use acute angle because it is easy to draw. But it is hard for mold makers to build every edge will acute angle. The acute angle on mold will be cracked easily and will hurt people like knife. Therefore unless it is necessary, all edges will be built with radius. The radius can be from 0.5 mm R to 2 mm R. If a radius is smaller than a general purpose cutter, a toolmaker needs to use a fine cutter to shape the area to form required radius. Sometime, it takes 3 times to achieve reguired radius.

The acute angle can not be produced by CNC machines. The toolmaker needs to use wire cut to produce acute angle or edge. Sometime, toolmaker will use laser cut or grinding machines to produce acute angle. The acute angle makes mold cost higher. It is better for product designers to specify the necessary acute angles on 2D drawing and add notes that all other areas can be with maximum radius such as 2 mm. The product designer shall try his best to add radius on his 3D model. It is because toolmakers make mold to produce part according to 3D model. They take codes from 3D and input codes into CNC machines. When making SLA or SLS prototype samples, the acute angle does not cause any trouble in the process. The product designer shall not verify his designer only based on SLS or SLA. A part with bigger radius will help material flow and reduce injection pressure and deformation. Therefore it is worth to pay attention on radius and acute angle. The return is handsome. For questions on radius or acute angle, please email us.