the design points of SMC/BMC mould

Ningguang Mould have abundant experience in making SMC/BMC/GMT mould,according to the characteristics of composite materials and our experience,we collect a few points of SMC mould and BMC mould design.

When designing the SMC/BMC mould,we need according to the dimensions of  product to design the mould cavity,besides,we need choose the  suitable steel according as the quality request of  product surface  and the quantity,in order to ensure the SMC productquality,we should pay attention to the shear edge and ejector system.

1.Parting Surface Design

In order to ensure  demoulding easily,the dimension of products, process easily,choosing parting surface should consider below principles:(①)simplifying the ejection mechanism to make the product eject easily,parting surface position should make the products left  at the lower mould as much as possible after SMC mould open;(②)To minimize the flash,avoiding to damage the appearance of products;(③)Make SMC mould manufacturing and mould parts processing easily;(④)When products have high precision request for the radial size,should consider the flash thickness  influence on the precision of product size,take vertical parting surface is easy to guarantee  precision of product size;(⑤)Ensure the strength of the products,avoiding  the angle and thin wall appeared in the products.

The parting surface design is very important,we should analyze parting surface at the begining,draw the parting surface,ensure the smooth demoulding and manufacturing easily.

2.Machining precision requirement

Machining precision for new smc mould have 3 factors:dimension tolerance,shape tolerance and surface roughness.Mainly have 2  factors:dimension tolerance and surface roughness.Roughly,dimension tolerance divided into:the overall dimensions and cavity dimension.This two dimension can have +/- 1.5mm tolerance,needn't very precision,but cavity dimension must be very precision,must be strictly controlled according to the drawing,generally not exceed 0-0.1mm.

3.SMC mould and BMC mould design

3.1  Draft design

In order to take out products smoothly,avoid to damage products during demoulding,when design SMC products,inside and outside surface that  along the demoulding direction all should have enough draft.

we should pay attention to aspects as below when design SMC mould:(①)when SMC mould have larger moulding pressure,draft angle of  inside surface  is greater than darft  angle of  outside surface.(②)common draft value is 1-1.5 degrees,also can be small to 0.5 degree.

3.2 shear edge design

Shear edge is interlocking part from upper mould and lower mould,generally,require to quench.During SM C moulding process,there  have burr on shear edge,burr is useless for the smc products,from this point,the gap of shear edge can be bigger,but if the shear edge is too bigger,material movement  and unloading can be occured,but this can be solved by adjusting the height of shear edge.when design shear edge,we need consider the gap and high.Shear edge is one of the most important factor in smc mould design,the size of shear edge is suitable or not  can directly affect the product moulding and are there have any defect,so it has strict requirement and control.

In our smc mould design,shear edge can be done straight or transverse,it's better we adopt the straight shear edge as much as possible.It have 2 advantages:(①)won't touch the appearance when we repair the shear edge。（②）reduce the projection area of the product,needn't to improve the  pressure  of press machine.

3.3  round angle

Corner better use round angle,right angle is easy to cause stress concentration, crack will be happened when have stress and shock vibration,mould will crack in the demoulding process due to  suppress internal  stress,impact strength of  products.In general,with radius of 0.5mm can greatly increase the strength  of products.Adopting the round angle have 2 advantages:(①)to avoid stress concentration,impove the products strength and aesthetic.(②)when quenching and working,mould won't crack due to the stress concentration.

3.4  heating method

SMC  mould temperature directly affects the product's quality and production efficiency,so smc mould need have heating system to achieve the ideal temperature.

Heating system can be divided into  electric heating,steam heating and oil heating.Electric heating is the most commonly used,its advantage is simple and compact equipment,less investment,installation and maintenance are easily,easy to adjust the temperature  and automatic control.

Steam heating,heating fast,temperature is uniform,but not easy to control,cost is  higher than electrical heating.

Oil heating,temperature is uniform and stability,heating fast,but will have work  enviroment  pollution.

According  to company's conditions and cavity size,cavity complexity factors to determine  choose which heating method.

3.5 choosing SMC mould /BMC mould steel

According to different production quantity,moulding method and processing object  to choose suitable mould steel.SMC  mould and BMC mould should choose free-cutting,compact structure and good property of polish steel.

P20,commonly used in injection mould,the quality is OK.

718,prehardened steel,better polishing,quality is better than P20.

1.2738,prehardened steel,suitable for high requirements,durable,good polishing,uniform hardness.

3.6  surface treatment

In order to improve the wear resistance and corrosion resistance on the surface of SMC mould and BMC mould,normally will do the surface treatment.

Chrome plated surface treatment is one of most used method,Chromium plating layer in the atmosphere have strong ability of  passivation,can keep metalic luster,won't occur chemically reactive in a variety of acid medium.Chrome plated have excellent wear resistance and high heat resistance,When air is heated to 500 degree ,its appearance and hardness still don't have any obvious variation。

Nitriding treatment can improve the wear resistance greatly.

3.7  Ejection plate thickness

Ejection plate thickness should be  according to  mould size,shape and weight. Generally the shickness not less than 30mm,otherwise will cause problem,such as deformation of ejection plate.

3.8 Heating holes

SMC mould heating holes distribution require the gap of heating holes and cavity  can't be too close  or too far,it;s better to keep 40-80mm.Heating holes distribution should be rare in middle,dense on both ends.if adopt electric heating,to electric,the number of  electric heating tube is a multiple of 3,at the same time,heating tube should exceed the distance of cavity edge.

Above information is only for reference.If you have any new project need make SMC mould,BMC mould and GMT mould,please don't  hesitate to contact.