CNC machine for turning, drilling, milling and grinding - Modern Equipment Review

The company recently introduced the Hardpoint 300, a CNC machine that combines turning, drilling, milling and grinding. It is a modular concept machine and can be configured with up to four main spindles and a variety of tooling combinations, depending on user needs. The machine can machine the front and rear faces of a single part; machine a single face on two parts simultaneously; machine the front and rear faces of two parts simultaneously; or machine a single face on four parts simultaneously.

The company says its product represents a flexible and economic machine concept for high-quality, complete machining of small components. The axes is variable, with up to ten possible. The machine offers fully automatic, synchronous complete cutting of complex workpiece geometries, up to a diameter of approximately 3" x 3" (80 mm x 80 mm).

The modular machine concept is said to ensure machining efficiency and flexibility. The various platforms are said to allow several cutting processes to be combined, thereby eliminating the need to operate multiple machines. The company says this reduces floor space requirements and operation costs. The machine incorporates an internal gantry loader. External loaders are also available as is a post-process measuring system.

Steering to greater flexibility: re-tool aging dedicated machines? For this plant, it makes more sense to spend a bit more to replace them with new, m

Sure, a dedicated machine delivers faster cycle times, but when it goes down, production stops until the machine is repaired. And for what it costs to re-tool that dedicated machine for another job, you can almost buy a new, more flexible, CNC machine that is better suited to today's production requirements." If you get the feeling from the above remarks that dedicated machine tools are on the way out at Visteon's Chassis plant in Indianapolis, Indiana, you're right.

The plant, which specializes in the production of power rack and pinion steering gear assemblies for passenger cars and trucks, has eliminated about half of the dial index machines used to produce input shafts, a critical component of a power steering valve. And as the input shaft jobs running on the remaining dial index machines end or change, the plant expects to retire them, rather than re-tool them, as well.

The input shaft is a cylindrical steel component, about 6 inches long by 1 inch in diameter, machined from barstock. It requires numerous operations, including an "Op 80," in which multiple holes (hydraulic fluid passages) are drilled through the OD to a main bore running the length of the part.
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At one time, the input valves were drilled almost exclusively on automatic dial index machines. Recently, however, the Visteon plant received an order for a new rack and pinion steering gear assembly with an input shaft that required an unusually small (1.5-mm diameter) hole. At a staff meeting to discuss the new job, the drill supplier advised that the small hole would have to be drilled at a higher rpm than the dial index machines were capable of, so the staff began considering alternate ways of producing the hole.

"We have a large number of dedicated machines in the plant, and there was a growing awareness that the time and cost involved in setting up the machines for different jobs greatly limited our efficiency and flexibility," explains Wahid Kapadia, a member of the Forward Models Engineering department. "We started looking for a CNC machine to drill the small hole for a number of reasons. First, many CNC machines offer the spindle speeds that we needed to drill the hole. Second, small drills are vulnerable to breakage, and CNC machines offer the tool control needed to minimize the problem.

"Third, we are very concerned about maintaining production rates," be continues. "When a problem arises on a dedicated machine, production stops and does not start again until the problem is solved. On the other hand, when production is spread over several standard CNC machine tools, if one machine develops a problem, the other machines continue to make parts, and although production is affected, it isn't completely stopped."

The plant first considered a CNC lathe with live tooling. However, it was unable to find a machine that offered the drilling speed required for the small hole.

Next, the plant looked at standard CNC drilling and tapping machines. Several such machines would be needed to satisfy the production volumes involved. However, because the machines would run in a largely unattended mode, some add-ons would be required to equip them for the job. One or more robots would be needed to automate the loading-unloading of parts. An indexing workholder would also be needed to index the input shaft in 90-degree increments for drilling. The prospect of buying the machines and fitting them with the workhandling equipment needed for the job was becoming daunting. A simpler solution was desired.

After more research, the plant investigated the A-Series machining centers made by Wasino Corp. U.S.A. (Rolling Meadows, Illinois). The A-Series consists of four-axis (X, Y, Z and C) machining centers with secondary turning capability. Configured more like automated turning machines than conventional machining centers, the series has a horizontal, 4,000-rpm spindle with a C axis that is programmable in 0.0001 inch increments. The spindle is served by a tool turret, which can accommodate a rotary or turning tool at each tool station.

The A-Series machines also feature an integral gantry loader that takes parts to be machined from, and returns machined parts to, a compact, carousel-like staging area at the rear of the machine. The machines come with chucks up to 10 inches (for the largest model) for handling discrete parts, as well as a spindle bore that permits feeding barstock or extrusions to the machine from a bar feeder.

One of the most important features of the machine to Visteon was that the tool turret could directly drive (with no gearing) rotary tools to speeds up to 10,000 rpm, providing the speed to drill the small hole needed for the new input shaft. Accordingly, the plant purchased the A-12 model (for 12 turret tools). To make certain that the plant would have adequate drilling speed for current and future jobs, it purchased the machine with a speeder head that doubled the maximum speed capability to 20,000 rpm

CNC multispindle - Spotlight: workholding

The company has recently introduced the MultiDeco 20/8b. This machine is configured for machining parts up to 20 mm in diameter. It has eight spindles and comes equipped with an integrated bar feeder. The machine is also available in a 2 x 4 configuration. This model can be a traditional eight-spindle machine, or a two four-spindle machine to produce two relatively simple, separate parts at the same time. The model is said to combine the advantages of cam-controlled and CNC machines through the use of TB-DECO software and its PNC control.

As an eight-spindle machine, this model can produce highly complex parts featuring cross milling/drilling with 23 simultaneous axes, six cross slides and spindle and counter-spindle stops, the company says. The counter spindle has two axes capability, permitting complete machining of a part. The machine features different spindle combinations, including single-speed, two-speed and two-speed with stopping.

Rapid Planning for CNC Milling-A New Approach for Rapid Prototyping

This paper presents a description of how CNC milling can be used to rapidly machine a variety of parts with minimal human intervention for process planning. The methodology presented uses a layer-based approach (like traditional rapid prototyping) for the rapid, semi-automatic machining of common manufactured part geometries in a variety of materials. Parts are machined using a plurality of 2 ½-D toolpaths from orientations about a rotary axis. Process parameters such as the number of orientations, tool containment boundaries, and tool geometry are derived from CAD slice data. In addition, automated fixturing is accomplished through the use of sacrificial support structures added to the CAD geometry. The paper begins by describing the machining methodology and then presents a number of critical issues needed to make the process automatic and efficient. Example parts machined using this methodology are then presented and discussed.

Keywords: CNC Machining, Rapid Manufacturing, Rapid Prototyping, Process Planning, Computer-Aided Manufacturing
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Introduction

The cost of producing small numbers of parts has been driven by the cost required to process-engineer the part(s). Traditional computer-aided process planning (CAPP) systems have reduced the time required to plan machined parts, but the cost for one or two-of-a-kind machined parts is still dominated by the cost of planning the part. The current use of CNC machining for these small quantities of parts is further limited by special tooling costs and machine setup.

The typical approach to planning parts for CNC machining has been to define the "features" of the part and match these features and tolerances to a set of processes that can create the required geometry to the specified accuracy. This approach has worked reasonably well for medium to high-volume parts, but it has had marginal success for the production of very small quantities of parts. In most cases, the time required to plan the part, kit the required tooling, and set up the machine (both fixture and tooling) has limited the use of CNC for these applications. The result is that rapid deployment of CNC machining has been relegated to a simple set of part geometries. The promise of minimal process engineering is a major factor that has driven the use of freeform rapid prototyping (RP) techniques. Unfortunately, many of these processes have been restricted to a small variety of materials with limited geometric accuracy.

In the literature, process planning is often approached with a set of goals driven by high production levels of parts-that is, a set of plans that strives for cost effectiveness through maximizing feeds and speeds and creating repeatable setups that can be paid for through economies of scale. Process planning for CNC machining includes tasks such as fixture planning, toolpath planning, and tool selection. There is a considerable amount of work in the literature pertaining to these three areas (Maropoulos 1995; Chen, Lee, and Fang 1998; Joneja and Chang 1999). The concept of flexible fixturing has been the topic of much research, though a completely autonomous fixture design system has yet to be developed (Bi and Zhang 2001).

Some exploration into the use of CNC machines for rapid prototyping has been published. Chen and Song (2001) describe layer-based robot machining for rapid prototyping using machined layers that are laminated during the process. The process is demonstrated using laminated slabs of plastic, machined as individual layers upon gluing to previous layers.

A hybrid approach using both deposition and machining called shape deposition manufacturing (SDM) continues to be developed (Merz et al. 1994). For each layer, both support and build material is deposited and machined in a combined additive and subtractive process. Sarma and Wright (1997) presented Reference Free Part Encapsulation (RFPE) as a new approach to using phase-change fixturing for machining. The approach was discussed recently in conjunction with high-speed machining (HisRP) (Shin et al. 2002). RFPE, in combination with feature-based CAD/CAM was proposed as an RP system (Choi et al. 2001).

Another approach is to use CNC machining for prototyping dies, an area called rapid tooling (Radstok 1999). One approach to rapid tooling uses machined metal laminates stacked to form dies (Vouzelaud, Bagchi, and Sferro 1992; Walczyk and Hardt 1998).

Many of these methods utilize CNC machining but do not address the fundamental problems of automating a fully subtractive rapid machining approach. This paper presents a method for "feature-free" CNC machining that requires little or no human-provided process engineering. The methodology described in this paper is a purely subtractive process that can be applied to any material that can be machined. The method described herein was developed in response to the challenge of automating as much of the process engineering as possible. The ultimate goal is to generate both the NC code and an automatically executed fixturing system by the touch of a button, using only a CAD model and material data as input. The process is perfectly suited for prototypes as well as parts that are to be produced in small quantities (~1 to 10)