Sheet metal forming using FDM rapid prototype tool

Purpose – The purpose of this paper is to investigate usage of fused deposition modeling (FDM)-based sheet metal tooling for small lot productions as a real case. FDM-based sheet metal tooling was used for stamping prototype parts for two different materials to evaluate dimensional conformance. Design/methodology/approach – The experimental process of data capture used the following steps: sheet metal parts were stamped and optically scanned at every 10th interval for both DC04 and S355MC material. FDM-based upper and lower dies were optically scanned at 1st, 51st and 101st intervals. Dimensional conformance analyses were carried out by using scanned data to evaluate the behavior of FDM dies against DC04 and S355MC materials in terms of geometric deviation. Findings – Satisfactory results were obtained for DC04 material by using FDM-based tooling, and overall deviation was at an acceptable level in terms of production tolerance. S355MC material is harder than DC04 and results were not convenient in terms of tolerance range. Geometric deviation of FDM dies was slightly increased and after the 50th part, increased drastically due to squeezing of FDM layers. Experiments showed that this method can be used for DC04 material and up to 100 parts can be stamped within the tolerance range. Using FDM-based sheet metal tooling, product development phase can be shortened in terms of leading time. Originality/value – This paper presents a study to create an alternative tooling method to shorten product cycle and product development phase by integrating rapid tooling methods to low-volume production.

A Framework for Explicating Formal Geometrical and Dimensional Tolerances Schema From Manufacturing Process Plans for Three-Dimensional Conformance Analysis

A process plan is an instruction set for the manufacture of parts generated from detailed design drawings or computer-aided design (CAD) models. While these plans are highly detailed about machines, tools, fixtures, and operation parameters, tolerances typically show up in less formal manner, if at all. It is not uncommon to see only dimensional plus/minus values on rough sketches accompanying the instructions. On the other hand, design drawings use standard geometrical and dimensional tolerances (GD&T) symbols with datums and datum reference frames (DRFs) clearly specified. This is not to say that process planners do not consider tolerances; they are implied by way of choices of fixtures, tools, machines, and operations. Process planners do tolerance charting in converting design tolerances to the manufacturing datum flow based on operation sequence, but the resulting plans cannot be audited for conformance to design specification. In this paper, we present a framework for explicating the GD&T schema implied by machining process plans. The first step is to derive DRFs from the fixturing method in each setup. Then, basic dimensions for features machined in the setup are determined with respect to the extracted DRF. Using shop data for the machines and operations involved, the range of possible geometric variations are estimated for each type (form, size, orientation, and position). The sequence of operations determines the datum flow chain. Once we have a formal manufacturing GD&T schema, we can analyze and compare it to design specification using the T-map math model.

The Effect of Thread Dimensional Conformance on Vibration-Induced Loosening

This paper presents the results from dynamic tests that investigate the effect of thread dimensional conformance of fasteners on vibration-induced loosening. Test specimens include combinations of bolts and nuts within dimensional conformance as specified by ASME Standard B1. 1-1992, as well as bolts with undersized pitch and major diameters and nuts with oversized pitch and minor diameters. Tests were performed using an inertial loaded compound cantilever beam apparatus that subjects the test fasteners to a vibration environment. Data from the tests show a significantly degraded resistance to vibration for the fastener combinations with undersized pitch and major bolt diameters or oversized pitch and minor nut diameters, compared to fastener combinations within conformance. Specifically, the lower 90 percent confidence limit for the time to failure for conforming specimens was 782 seconds compared to 8 to 29 seconds for nonconforming specimens.