Drilling crankshafts a whole lot better

Drilling crankshafts a whole lot better

Machining system improves oil-hole precision and optimizes crankshaft manufacturing.

Emag HSC series systems optimize crankshaft-oilhole drilling through special machine designs that allow using short tooling, multiple-part drilling and self-contained work handling.

Because HSCs drill crankshaft oil holes from below, as opposed to transfer-type systems that do it from the top or sides, chips fall freely away from the machining area and into chip conveyors, so shops don't have to peckdrill oil holes.

The workpiece-handling system on the HSC does not interrupt crankshaft machining or require additional axes, and they shorten loading-traverse distances for fast chip-to-chip times.

Oil holes deliver vital lubrication to contact points between piston connecting rods and crankshafts in truck and car engines. Because oil holes are interconnected, they must enter and exit crankshafts at precise positions for efficient lubrication, or the engines will fail.

To prevent such failures, machine tool builder Emag Maschinenfabrik GmbH researched the capabilities of existing tooling and then determined the optimum oil-hole-drilling process as far as tool lengths, coolant types, cutting parameters and other relevant factors are concerned. As a result, the company developed the HSC series of manufacturing systems and an optimum drilling process involving the shortest drills possible and minimal-quantity lubrication, both of which increase tool life and drilling speed for diameters between 4 and 8 mm.

Crankshafts for the automotive industry are made of heat treated and hardened wrought steel with tensile strengths up around 1,100 N/mm2 and measure from 300 mm in length and 190 mm in diameter for three and four-cylinder passenger-car engines to 1,500 mm in length and 330 mm in diameter for truck engines. Crankshafts for truck engines can weigh as much as 200 kg.

Typically, shops machine oil holes in multispindle drilling operations using drill bushings and tools with length-todiameter ratios of more than 20:1. However, Emag says the feedrates, tool lives and flexibility of these systems no longer satisfy the demands of today's automotive suppliers.

The company reports that its HSC manufacturing systems quickly and precisely drill oil holes and end-machine crankshafts while delivering longer tool lives when compared with conventional systems. HSCs also lower unit production costs and shaft-rejection rates for crankshafts measuring from 190 mm in diameter and 300-mm long to 330 mm in diameter and 1,500-mm long. To handle various crankshaft weights and sizes, the machines come in two frame sizes.

Crankshafts are one of Emag's " strategic parts" that it focuses on when building complete machining lines starting with modular platforms. Modular platforms , which include the VSC, HSC, VTC, VLC and other machines, let Emag start with similar building blocks that are shared among the platforms and then simply add components that will engage workpieces to reduce machine costs for customers.

"Most OEMs build a machine tool and then adapt it to a customer's specific part," says Gary Hulihan of Emag's U.S. facility in Farmington Hills, Mich. Because of its modular platforms, Emag builds machines around a customer's specific part.

As a result of this mindset, the company's HSCs for crankshaft machining do several operations in single setups to consolidate process streams. These operations, besides pilot and oil-hole drilling, include deburring, chamfering and gaging for crankshaft drilling and milling, countersinking, threading and gaging for end-machining work.

According to Hulihan, the HSC's overhead setup puts tooling close to crank-shafts, allowing shops to use shorter drills than those of other systems. The machine moves crankshafts to the tooling, which is stationary and vertically oriented below workpieces on a U axis that tilts at any angle for drilling oil holes. Orienting crankshafts above tooling, as opposed to transfer-type systems that drill from the top or sides, also lets chips fall freely away from the machining area and into chip conveyors and eliminates having to peck-drill oil holes.

Shops usually manufacture crankshafts in serial production, first green machining them prior to heat treating and then, afterwards, hard machining. Green machining involves cutting journals, main bearings and counter weights and cheeking if needed. While most shops drill oil holes when shafts are in the green state, Emag is working with some customers that are increasing accuracy by drilling shafts after they've been hardened. Such an operation demands machine rigidity, and for this, Emag's machines rest on bases made of the company's special Mineralit polymer granite that dampens vibration and provides thermal stability.

The company's gantry-type machine designs feature centrally supported headstocks and triple guideways in Z located above and, therefore, outside machining areas. The gantry design, along with the polymer granite bases, increases machine rigidity and process integrity and helps extend tool life.

Depending on crankshaft specifications, shops can machine with one tool or two or three tools simultaneously on an HSC. The machine houses as many as three spindles mounted side-by-side for six times higher output rates. Emag claims it's the only builder who is supplying pick-up machines for oil-hole drilling and end-machining work on crankshafts.

Because crankshafts clamp between workholding units and tailstocks and move to tooling, HSCs load themselves without using gantry loaders, robots or other workpiece-transport systems. Operators insert crankshafts into carrier prisms on loop conveyors that transport the shafts to pick-up stations where they are clamped and taken into machining areas. Workpiece-handling systems such as this do not interrupt machining or require additional axes. They also shorten loading traverses and speed chip-to-chip times.

Typically, parts load directly into machines with overhead gantry systems. Unfortunately, once a machine finishes a shaft, it has to stop, unload the finished part and load a new one, all of which increases chip-to-chip time.

To ensure quality, HSC control systems record all finished crankshaft dimensions, which are checked while workpieces — even massive truck crankshafts — remain chucked. This, in turn, lets shops quickly generate authentic acceptance protocols.

For more information on process optimization...visit americanmachinist.com

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