When I started my career in metalworking 28 years ago, machine shops were in a transformational period. Small shops still relied heavily on conventional machine tools and the skill of the craftspeople who ran them. But CNC machine tools were becoming affordable, and these shops quickly were adopting the technology.
Automation and productivity always have been the most significant attributes of CNC equipment, and they were the primary selling points in the early days. It was multi-axis interpolation, or the ability to drive a cutting tool through curves and angles, that became the foundation of the next series of technological advances. Machine tool builders realized that low-volume shops were an untapped market, so builders started looking for technologies that would be advantageous. Simplified programming was considered a feature that would allow machine tool builders to penetrate the small-shop market. Machine tool builders began introducing technologies like conversational controls and easy-to-use canned cycles, which made programming easier and allowed small shops to transition to CNC machine tools.
Advances in CNC programing also included affordable graphical CAM software that is now common at all types of machine shops. Before the advent of graphics-based CAM packages, programmers would write code by hand, copy and edit existing programs or use complex text-based CAM programs. Advancements in programming have significantly improved productivity and made the creation of complex geometries easy.
These changes in CNC technology profoundly impacted the way that cutting tools were manufactured and how tool and cutter grinding was performed.
When I started programming in 1993, cutting tools were not much different from those of the 1960s. Tools and machines were designed to take deep, heavy, high-horsepower cuts, and complex geometries often were created using form tools. Before CNC machines, form tools were the standard method for creating complex geometries, so their use on the first CNC machines was a natural progression.
Using form tools to generate complex geometries was especially normal for large manufacturers, which frequently had rooms full of tool grinding equipment, along with teams of craftspeople to operate the machinery. Companies that did not make their own tools could easily find local shops that specialized in cutting tools.
Form tools have several benefits. The tools combine operations, reducing cycle times and the number of inputs needed at machines. Most importantly, form tools decrease opportunities for mistakes. But the tools can increase lead times for part introductions, inflate inventory costs and become obsolete with engineering changes.
Market conditions and concepts like lean manufacturing have altered the way that parts are manufactured. The desire to reduce inventory costs has driven reductions in manufacturing lot sizes and demanded lower lead times. Success in these changing conditions requires shops to be agile, and using custom tools can inhibit agility.
As machine tool programming advanced, machine shops began to migrate away from complex form tools. It is now common for engineers and programmers to rely on modern CAM systems that use off-the-shelf cutting tools to create complex geometries. An example is cutting O-ring and lock ring grooves on a lathe. Groove geometry for O-rings and lock rings varies with each part. In the past, a tool would be ground to the exact shape of a groove, making the tool part-specific. It is possible today to use a single indexable tool to make an infinite number of groove shapes through modern programming techniques. This eliminates the need for custom tools, inventory, maintenance costs and the possibility of obsolescence.
CNC advancements modified not only work at the machine shop but the way that cutting tools are manufactured. Before, tool grinding shops both large and small relied on highly skilled craftspeople. The people who make cutting tools are some of the most talented individuals in manufacturing. Tool grinding with conventional machines takes years to master. Craftspeople had to learn how to set up and operate complex tool grinding machines, as well as understand machining, to make tools that would cut well. These workers also had to be proficient with trigonometry and geometry so they could set up machines to create complex shapes.
Old tool and cutter grinding equipment had a number of places to adjust the angle of a tool so it would be presented correctly to the grinding wheel. A tool with multiple steps, angles and radii required numerous setups, all done by hand. Making more than one tool also meant batch processing after each new setup. The work could be very tedious, and a single wrong setup might scrap a whole batch of tools. Additionally, cutting tool designers faced limitations because they had to be careful not to specify geometries outside the capabilities of a grinding machine.
With their advanced programming techniques, CNC tool and cutter grinders revolutionized cutting tool manufacturing. The ability to control multiple axes and program complex grinding paths permitted tool designers to create cutting tool geometries that have challenged milling and turning machine tool builders to keep up.
Advanced endmills are the best example. Over the past few years, there has been an arms race in the cutting tool industry, with toolmakers offering things like variable pitch geometry and variable helix geometry. These advances would have been close to impossible without modern grinding equipment.
Cutting tool companies also have benefited from things like reduced lot sizes, greater flexibility and faster setups. Productivity has been enhanced because one person can tend numerous machines. Multiple setups are less frequent, with most tools being made in one setup and thereby increasing quality. Most substantially, advanced machines have automated the tedious aspects of cutter grinding and allowed toolmakers and engineers to focus on chip formation theory, reducing the lead time of new designs.
Advancements in CNC machines and programming have altered the way that manufacturers make and use cutting tools. Cutting tool manufacture and maintenance for most machine shops now is outsourced to companies that specialize in cutting tools. Engineers and toolmakers are focused on chip formation theory, and grinding machine dynamics are no longer the limiting factor in cutting tool design. The next wave of advances likely will involve cutting tool materials and the abrasive tools used to manufacture them.
Related Glossary Terms
Substance used for grinding, honing, lapping, superfinishing and polishing. Examples include garnet, emery, corundum, silicon carbide, cubic boron nitride and diamond in various grit sizes.
- computer numerical control ( CNC)
computer numerical control ( CNC)
Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.
- computer-aided manufacturing ( CAM)
computer-aided manufacturing ( CAM)
Use of computers to control machining and manufacturing processes.
- cutting tool materials
cutting tool materials
Cutting tool materials include cemented carbides, ceramics, cermets, polycrystalline diamond, polycrystalline cubic boron nitride, some grades of tool steels and high-speed steels. See HSS, high-speed steels; PCBN, polycrystalline cubic boron nitride; PCD, polycrystalline diamond.
- gang cutting ( milling)
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.
- grinding machine
Powers a grinding wheel or other abrasive tool for the purpose of removing metal and finishing workpieces to close tolerances. Provides smooth, square, parallel and accurate workpiece surfaces. When ultrasmooth surfaces and finishes on the order of microns are required, lapping and honing machines (precision grinders that run abrasives with extremely fine, uniform grits) are used. In its “finishing” role, the grinder is perhaps the most widely used machine tool. Various styles are available: bench and pedestal grinders for sharpening lathe bits and drills; surface grinders for producing square, parallel, smooth and accurate parts; cylindrical and centerless grinders; center-hole grinders; form grinders; facemill and endmill grinders; gear-cutting grinders; jig grinders; abrasive belt (backstand, swing-frame, belt-roll) grinders; tool and cutter grinders for sharpening and resharpening cutting tools; carbide grinders; hand-held die grinders; and abrasive cutoff saws.
- grinding wheel
Wheel formed from abrasive material mixed in a suitable matrix. Takes a variety of shapes but falls into two basic categories: one that cuts on its periphery, as in reciprocating grinding, and one that cuts on its side or face, as in tool and cutter grinding.
Process of generating a sufficient number of positioning commands for the servomotors driving the machine tool so the path of the tool closely approximates the ideal path. See CNC, computer numerical control; NC, numerical control.
Turning machine capable of sawing, milling, grinding, gear-cutting, drilling, reaming, boring, threading, facing, chamfering, grooving, knurling, spinning, parting, necking, taper-cutting, and cam- and eccentric-cutting, as well as step- and straight-turning. Comes in a variety of forms, ranging from manual to semiautomatic to fully automatic, with major types being engine lathes, turning and contouring lathes, turret lathes and numerical-control lathes. The engine lathe consists of a headstock and spindle, tailstock, bed, carriage (complete with apron) and cross slides. Features include gear- (speed) and feed-selector levers, toolpost, compound rest, lead screw and reversing lead screw, threading dial and rapid-traverse lever. Special lathe types include through-the-spindle, camshaft and crankshaft, brake drum and rotor, spinning and gun-barrel machines. Toolroom and bench lathes are used for precision work; the former for tool-and-die work and similar tasks, the latter for small workpieces (instruments, watches), normally without a power feed. Models are typically designated according to their “swing,” or the largest-diameter workpiece that can be rotated; bed length, or the distance between centers; and horsepower generated. See turning machine.
- lean manufacturing
Companywide culture of continuous improvement, waste reduction and minimal inventory as practiced by individuals in every aspect of the business.
Any manufacturing process in which metal is processed or machined such that the workpiece is given a new shape. Broadly defined, the term includes processes such as design and layout, heat-treating, material handling and inspection.
Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.
1. On a saw blade, the number of teeth per inch. 2. In threading, the number of threads per inch.
Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.
- turning machine
Any machine that rotates a workpiece while feeding a cutting tool into it. See lathe.