Document Type

Thesis - University Access Only

Award Date

2004

Degree Name

Master of Science (MS)

Department / School

Industrial Management

First Advisor

Huitian Lu

Abstract

The Recurrence Casting (RC) process is a relatively new technique for the manufacturing of profile products such as doorframes, panels, and sidings. The RC process is preferred to aluminum extrusion for short production runs and custom made designs. The many benefits of the RC process include reducing pre-processing methods, shortening lead-time, and reducing initial setup cost for small productions runs and custom designs. But one of the major concerns when applying the RC process is the surface quality of the plastic profile. The different kinds of surface finish defects observed are joint effects, polymer flow on the sides of the profile, burrs, and so on. The objective ve of this exploratory research was to investigate the surface finish quality of RC products and to investigate the ability of silicone rubber to reproduce the surface finish of the master model and its effects on the surface finish of the RC products. To identify the factors affecting the RC process, a Design of Experiment (DOE) was designed for determining the factors affecting the plastic profile pulled by the RC equipment. Specific parameters evaluated included speed of the leadscrew, injection time delay, layer thickness, surface finish of the mold cavity, surface finish of the master model, and volume of the mold cavity. These factors were classified into controllable and un-controllable variables. Since the RC process is in the preliminary stage of development, certain factors like layer thickness, volume of mold cavity, simultaneous injecting of polymer and rotation of leadscrew were considered uncontrollable because there was no equipment available to control the factors. The major factors considered for experimentation are speed of leadscrew and delay time. The RC equipment was run at different level combinations, and the sample plastic profiles were pulled. The sample plastic profile was measured for the surface finish using a pocket-surf profi lometer. The measured response from the different treatment combinations of the factors and levels were tabulated. The tabulated responses of the surface finish of the plastic profile were used to analyze the data using DOE techniques. The results were statistically analyzed to determine the significant factors and their interactions. A total of 13 trial runs were conducted, and there were 2 responses, the 'joint" and the "middle" effects. The DOE was designed such that the trial runs had two 2x2 full factorial and 2 replicates with 5 center points. The 2 full factorial design responses with the same levels were averaged, and then they were augmented with 5 center points to perform Response Surface Method (RSM) analysis. In addition, a 2x2 full factorial design with 2 replicates was used to perform a full factorial design. The same procedure was followed to perform DOE for the other response "middle" effects. From the analysis, it was concluded that delay time was significant in affecting the surface finish of the plastic profile. For the "middle" effects it was observed that there was some kind of interaction between delay time and speed of leadscrew, and it did not show any conclusive evidence to make formative statements. It was concluded that in determining surface finish effects on plastic profile for the location 'B' more factors and trial runs needed to be considered. Since the delay time is the factor affecting the surface finish of plastic profile at location 'A', it is important to have good balance between the delay time and movement of platform such that, as the polymers are injected into the mold it should give the polymers the time to transform itself from liquid to solid state and also the platform is to be moved synchronous with delay time and thereby avoiding any static in the process for the injected polymer in the mold. Keeping in mind the critical specification for polymers, the gel time, and demold time, the platform is to be moved in synchronous with injection of polymer. By implementing advanced technologies like servomotors, pneumatics, motion controllers, hydraulics, etc. to the leadscrew and for mixing and injection of polymer, a two chamber with high speed mixing and injecting pump is to be used. These advanced technologies can be used to control the injection of polymer and movement of platform precisely as per requirements to avoid joint effects on the surface finish of the plastic profile.

Library of Congress Subject Headings

Plastics -- Molding -- Quality control.
Injection molding of plastics.
Surfaces (Technology)
Rapid prototyping.

Publisher

South Dakota State University

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Rights Statement

In Copyright