Successful development of innovative and dynamic parts in today’s miniature dental and medical components industry presents a formidable and equally dynamic challenge to cutting tool manufacturers.
The fast-growing field is driven by enterprising orthopaedic surgeons and dental professionals together with medical screw and implant companies, who work in close cooperation with computer aided design and manufacturing (CAD/CAM) software developers and dedicated machine and tool manufacturers to transform their inventions into parts that are revolutionising medical and dental procedures. Each new component demands correspondingly advanced tools and geometries to create the new and complex shapes, and to ensure extreme precision and consistently excellent surfaces.
The materials used for producing medical screws and implants are titanium superalloys, although stainless steel hard materials are used when a special ratio of depth of cut to chip thickness is required. These materials are gummy and cause built-up edge (BUE), which tends to wear down edge sharpness, while the high temperatures generated during chip breaking shorten tool life and damage surface quality.
Iscar, a manufacturer of cutting tools for metalworking has invested time and resources to develop optimal machining solutions for the medical sector, applying unique geometries, tools and grades. Utilising CAD/CAM systems to create custom tool assemblies according to the ISO 13399 standard, Iscar developed cutting tools for machining miniature medical parts, specifically dental screws and four components for hip joint replacement implants: Femoral head, acetabular shell, femoral stem and bone plate.
Iscar provides dedicated cutting tools for each of the main operations involved in machining dental screws.
Iscar developed two options for rough OD (outer dimension) turning. The SwissCut compact tool is designed for Swiss-type automatics and CNC lathes, and enables reduced setup time and easy indexing without having to remove the toolholder from the machine, while the inserts are equipped with chip deflectors designed specifically for machining small parts.
The second option features SwissTurn toolholders, with a unique clamping mechanism to optimise insert clamping and replacement on Swiss-type machines, and JetCut high pressure coolant tools. SwissCut tools are used for the turn threading operation.
ChatterFree endmills are utilised for the slot milling stage to maximise stock removal rate, eliminate vibration and reduce cycle time. The unique ground geometry provides excellent surface and tool life, while machining at high material removal rates.
PentaCut parting and grooving inserts perform the cut-off operations. With five cutting edges and very rigid insert clamping, PentaCut is a stronger insert for higher machining parameters particularly on soft materials, parting of tubes, small and thin-walled parts.
SwissCut tools are used in the face and OD turning (screw head turning) operation while the drilling operation is performed by SolidDrill solid carbide drills with 3xD and 5xD drilling depths and right-hand cut. The drills feature coolant holes.
The thread milling operation features SolidThread thread mills, whose short 3-tooth cutting zone with three flutes and released neck between the cutting zone and the shank enable precise profiles and high performance. The extremely short profile exerts a low force, which minimises tool bending, facilitating parallel and high thread precision for the entire length.
Solid carbide SolidMill endmills with two flute, 30° helix medium length, perform the key head milling operation.
Hip joint replacement
Complex operations are involved in machining components for hip joint replacement, which demand high accuracy, pristine surface quality, and absolute reliability. Iscar provides products for each operation to maximise their precision and efficiency.
The machining required for a femoral head involves rough turning or rough grooving, semi-finish profile turning, rough drilling, semi-finish milling, semi-finish internal turning, internal grooving (undercut), cut-off, rough turning, and semi-finish turning.
IsoTurn turning tools may be used for rough turning. The ISO standard tools perform most of the industry’s chip removal in applications ranging from finishing to roughing. Offered in all standard geometries, the trigon (semi-triangular) turning inserts for axial and face turning features six 80° corner cutting edges. For profile machining, Iscar provides intricate and precise V-Lock V-shaped special profile grooving inserts for the range of 10mm to 36mm. Precision ground and utility Cut-Grip full-radius inserts are used for performing semi-finish turning.
SumoCham drilling tools perform the rough drilling operation, offering fast metal removal and economical indexing with no setup time. SumoCham integrates a clamping system that enables improved productivity output rates and a shank designed with twisted nozzles, and a durable and stable body.
ChatterFree four flute endmills are utilised for the semi-finish milling operation. The endmills feature 38° helix and variable pitch for chatter dampening with 3xD neck relief. ChamGroove internal grooving inserts are applied for semi-finish grooving. The inserts possess extremely small bore diameters starting at just 8mm (the other diameters are 11mm and 15mm) and incorporate internal coolant.
Semi-finish internal turning is performed by IsoTurn inserts with SwissTurn toolholders, while the cut-off operation uses Do-Grip twisted double-sided parting inserts which feature double-ended twisted geometry for no depth of cut limitation.
For rough turning, the SwissTurn ISO standard insert range with small shank sizes is used. Also available for this operation are standard geometry inserts with precision ground cutting-edges and small radii for manufacturing small and thin parts.
The semi-finish turning operation is performed by using Cut-Grip inserts. In addition to the large variety of general use precision ground and utility inserts in the Cut-Grip family, there is a vast range of inserts for specific applications and materials.
Machining of the acetabular shell component consists of rough internal turning, finish profile milling, shouldering, upper and bottom chamfering, drilling, thread milling, external rough turning, and external grooving operations.
Heli-Grip double-ended inserts are used for the rough internal turning operation, as the twisted design allows them to groove deeper than the insert length. Internal finish milling is performed by SolidMill three flute, 30° helix short solid carbide ball nose endmills. SolidMill endmills with 4 flutes, 38° helix, and variable pitch for chatter dampening, perform the finish shouldering operations, as well as the special-shaped endmill which performs the upper and bottom chamfering operations that follow the drilling stage.
SolidDrill solid carbide drills with 3mm to 20mm range and 3xD and 5xD drilling depths are used for the drilling operation. SolidDrill tools feature a right-hand cut with and without internal coolant nozzles and advanced TiAlN coating for optimum hole quality, high performance reliability and economical output.
Thread milling is performed by SolidMill solid carbide internal threading endmills, which integrate coolant holes for ISO thread profiles. ISO standard inserts with SwissTurn toolholders feature JetCut high pressure coolant are used for rough turning and external grooving is performed with Cut-Grip precision inserts.
SolidMill endmills with four flutes, 38° helix and variable pitch for chatter dampening with 3xD relieved necks and SolidMill three flute, 30° helix short solid carbide ball nose endmills perform the final milling operations.
Machining the femoral stem involves slotting, spot milling, drilling, chamfer milling, turning, face and profile milling operations.
Multi-Master endmills with indexable solid carbide heads in the diameter range of 12.7mm to 25mm are used for the slotting operation. The endmills feature no setup time and a carbide thread connection for quick change, and conical and face contact for high precision and rigidity.
Spot milling is performed by means of SolidMill endmills with four flutes, 38° helix and variable pitch for chatter dampening with 3xD relieved necks. The drilling operation uses SolidDrill solid carbide drills. Chamfer milling is performed using Multi-Master endmills with indexable solid carbide heads in the diameter range of 9.1mm to 20mm. ISO standard geometry inserts with precision ground cutting edges are used with SwissTurn toolholders featuring JetCut high pressure coolant for the turning operation.
SolidMill three flute, 30° helix short solid carbide ball nose endmills with a 3mm to 25mm diameter range are employed for the profile milling operation, and SolidMill endmills with four flutes, 38° helix and variable pitch for chatter dampening with 3xD relieved necks with a 1.6mm to 8mm diameter range are utilised for face milling.
The machining required to manufacture a bone plate involves rough and finish milling, shouldering, drilling, and mill threading.
For rough milling, the FinishRed endmill geometries allow the tool to perform roughing and finishing operations at the same time. The result is the ability to apply roughing machining conditions, while obtaining excellent surface finish. Multi-Master interchangeable solid carbide tapered heads are applied to the finish milling operation, whereby the curved surfaces can be machined by tilting the tool and applying a large corner radius at small cutting depths. Shouldering is performed with ChatterFree endmills which enable high material removal rates, eliminate vibration, and reduce cycle time.
For the final milling stage, Multi-Master four flute, 30° helix short solid carbide ball nose endmills in the 5mm to 25mm range are employed, while SolidDrill solid carbide drills with no coolant holes and 4xD drilling depth are used to ensure stable and accurate drilling. SolidThread 55° or 60° profile solid carbide taper thread mills are used for the mill threading operation.
Grades specifically designed for machining applications on stainless steel and super alloys such as IC900, IC907, IC806, IC908, IC328, and IC928 are ideal for milling and turning titanium and nickel based alloys, such as Nitinol, commonly found in medical components. These grades are available for Iscar standard tools with specially designed positive and sharp edged chipformers.
It is no small challenge to manufacture miniature parts for dental and medical devices but Iscar has succeeded in developing highly effective cutting tools for this field that adhere to the stringent standards of quality and precision essential for medical industry applications.
For further details contact Iscar South Africa on TEL: 011 997 2700 or visit www.iscar.com