Journal of Mechanical Working Technology最新文献

This paper describes the computer-integrated design, fabrication and inspection of a 3-D curved surface as part of a wider study into the creation, machining and measurement of free-form surfaces. Using the CATIA solid modeller, a 3-D curve was first created using both a single arc and a spline followed by a surface patch. The surface generated by the two spline curves was faceted in appearance when machined, whereas that of the single arcs was smooth. An NC part program was generated interactively with dynamic, on-screen tool path display. However, because it was inconvenient to change the machining parameters, such as feedrate, within the NC program, a custom macro was written to make the NC program more readily modifiable. Machining tests carried out on aluminum and carbon steel test specimens yielded encouraging results. In the computer-assisted measurement of the surface on a CNC CMM, the VDA (Verband der Automobilindustrie Surface Data Communication Interface was adopted as the medium for data exchange between the CAD/CAM system and the CNC CMM. Instead of the SURF (surface) function, measurement was accomplished using a sequence of discrete measurement points, PSET.

This paper is concerned with tool management in autonomous manufacturing systems. On-line wear sensing, automatic decision making for tool replacement, and real-time optimization of cutting processes are focused on the turning problem. An adaptive control system designed to cope with this problem is described and discussed with application on the shop floor.

The data base has been used for accounting, inventory and record keeping as well as in certain applications in process planning, group technology coding, and computer aided design. In this research a relational data base was used in conjunction with a rule based system to select cutting tool geometry and machining parameters. This hybrid system consists of a supervisory program which selects the appropriate rule based system from the user provided input (such as milling, drilling, boring, or turning) which in turn searches the data base utilizing the data base manager. Although designed as a stand alone package it can be easily incorporated within a CIM system and integrated with CAD/CAE/CAM package(s) at a later date.

In this investigation a simple theoretical analysis of the solid compression test has been carried out so that the friction factor can be estimated quantitatively from the reduction-capacity test— the latter involves the compression of a cylindrical billet between flat parallel platens, using an energy-bound machine. Detailed experiments have been carried out on Armco iron to determine the friction factor using both the reduction-capacity test and the ring-compression test, in order to be able to obtain a comparative assessment of these two test methods. The results of the investigation indicate that if an aspect ratio of 2 or 2.5 is chosen in the reduction-capacity test, the friction factor corresponds with those obtained from standard ring-compression tests.

In this paper, the critical conditions for defect formation in the final stage of cup-cup axisymmetric combined extrusion are derived, using the upper-bound approach. The analytical results show that cracks may occur on the outer circumferential surface of the bottom of the billet and on the inner surface of the billet near to the corner of the lower ram. The critical relative thickness of the bottom of the billet during crack formation is affected mainly by the combination of the reduction in area of the forward-extrusion part and that of the backward-extrusion part. The relative dimensions of the defects vary with the reduction in area and with the relative thickness of the bottom of the billet. The results computed agree very well with experimental data.

The introduction of high tensile steel sheet to permit the use of thinner gauge in large pressings has increased the occurrence of the forms of elastic distortion known as springback and side-wall curl, and has increased, likewise, the need to control these by appropriate changes to the selection of process parameters when they lead to an unsightly product, or, more significantly, to a product in which loss of dimensional accuracy causes loss of function. They may also affect manufacture by making the stripping of the tooling more difficult. The use of thin sheet of high unit cost has increased the need for protection by zinc or aluminium/zinc (galvalume) coatings, and their effect on springback and side-wall curl under conditions appropriate to the pressing of large shallow panels is the subject of the present investigation. It is concluded that the resulting modification of friction does not significantly change the behaviour of steel sheet. Generally, any change in friction which increases the transverse stress gradient increases springback and side-wall curl.

It appears that differences in the reported effect of tool geometry on springback and side-wall curl can be attributed largely to differences in the rate of work hardening of the sheet tested.

It is confirmed that springback and side-wall curl increase with yield strength and work-hardening rate and with tool radius and tool clearance.

The purpose of blocking (reducing the ingot cross section) in open-die press forging is to maximize the internal deformation for better structural homogeneity and soundness of material in the core of the ingot. Forgings of high quality can be produced by specific control of the blocking parameters, e.g. die width, die configuration, die overlapping, die staggering, ingot shape, temperature gradient, draft design, pass design, etc. Physical modeling experiments, using plasticine as an easy-to-deform model material, have been conducted to study the effects of these blocking parameters on the deformation distribution in the forged ingots subjected to multiple-stroke blocking. To facilitate the multiple-stroke blocking study, new techniques had to be developed for better bonding between the layers of the plasticine specimens as well as for measuring the deformation strains in three dimensions from a single specimen. The evaluation of results shows substantial improvement in the internal-deformation distribution when the above-mentioned blocking parameters are optimized. This research work has resulted in providing better basic understanding of blocking parameters on centerline consolidation and product quality. Application of the laboratory modeling results to production forgings is reviewed also.