Injection Moulding

Dear all,

I work in injection moulding industry as a quality engg i have a doubt.I found some of my parts are often having a problem of warpage or bend and most frequently in heat condition i have studied in packing methods process but i have a doubt in material properties.

Material used : PPT 20%

Grade : HT 340

The elongation percentage for the material is 18%.But all my parts are not having the problem some of the parts we have bend or warpage. Let me know any valid reasons.