The appearance element of a professionally produced injection mould should also not contain traces of the moulding process, i.e. traces of defects. The appearance element here refers only to the traces formed on the injection moulded part by the mould design and does not contain traces of defects. For example, if a spot sprue is selected and no other sprue is selected, the traces of the spot sprue will be very small. If the fixed release type of construction is chosen, the aim is to place the gate on the inner surface of the injection moulded part, while if no release marks are wanted on the injection moulded part, the injection moulded part can take the push plate type of construction. The aim is to make the injection moulded part more aesthetically pleasing, which is the "appearance " element of the injection moulded part. Defects on the injection moulded part are also a key factor in determining the structure of the injection mould. Defects can affect the selection of the parting surface of the injection moulded part, the use of the core and exit mechanism, the design of the custom mould pouring system and temperature control system by the injection moulding processors, as well as the entire structure of the injection mould. Due to improper placement of the injection moulded part in the mould, some of these can cause imbalances in the melt filling flow field, producing defects such as flow marks, uneven distribution of internal stresses, underfilling and fusion marks.