(Q): How will the tool be qualified and how will the production parts be inspected:

(A): If your customer is only interested in parts that work, duplicate sets of gauges that are exchanged every six months between your QC and his incoming inspection department will avoid unnecessary false rejects. Once you have got the job, make sure everyone knows the definition of a good part. This will avoid wasted production, false rejects, and miscommunication.

(Q): What are problems in PIM (Powder injection moulding)?

(A): PIM is a newer manufacturing technology that has undergone considerable maturation and growth during the past five years. The field is aligned with the evolution of advanced materials, formed to net shapes, as used in many consumer products. The overall industry growth is strong and expanding rapidly, with currently about one new entry in the business every few weeks. Customer complaints on PIM largely focus on the lack of standards and poor quality. On the other hand, PIM moulders complaint that their customers have a poor understanding of the process. A consistent problem in the industry is long lead times in obtaining tooling. Many large-volume products have not been placed in the PIM industry because of problems like quality, capacity, and lack of multiple vendors. New rapid tooling technologies have reduced the time to first tooling to three days. PIM equipment is also evolving to a more desirable level of standardization, with several vendors now offering PIM grade moulding machines, debinding devices (solvent, vacuum, thermal, and catalytic), and continuous sintering furnaces.

Q): How to control surface roughness of extruded LLDPE?

(A): In many polymer process, the rate of production is limited by the onset of flow instabilities. During extrusion, for example, the extrudate becomes distorted at a critical throughput rate, typically when the shear stress applied on the melt exceeds the critical stress value of the material. This distortion varies in intensity and form, and is generally classified as surface irregularities (surface melt fracture). In a more severe form promoted by an increase in extrusion rate, or by a decrease in temperature, such surface melt fracture is often observed as "sharkskin." Sharkskin is characterized by the appearance of fine scale surface irregularities (transverse ridges similar to the design of tire tread), in the order of less than one-tenth the diameter of the extrudate. A number of techniques have been used for delaying or eliminating surface melt fracture. For example, an increase in processing temperature or film blowing processes has been effective in delaying the onset of surface melt fracture toward higher apparent shear rates. Such improvement has also been achieved by changing the metallurgy of the die. Another option, which has been very popular, is the use of process aids to change the polymeric melt rheology and alter interactions of the polymer melt with the extrusion die surface.

Courtesy: Mr. P.M. Jariwala, Kolsite Industries