HDT has extensive cold hobbing capabilities. We can create customer name, part ID, or grade markings in steel punch inserts by forming the feature instead of machining it. This creates a stronger, longer lasting and better polished finish than conventionally machined or EDM’d products.
Cold hobbing not only produces a finer detailed product, but in most scenarios, is more cost-effective than its EDM’d equivalent. In addition to the cost benefits, the life cycle of a hobbed part is much longer than that of an EDM’d part.
The process of cold hobbing takes a very hard piece of steel, previously engraved or embossed with specified details, known as the master hob, and pushes it into an unhardened steel blank by way of hydraulic press. This produces a hob with a reverse image of the specific details either impressed or raised on the blank depending on the job requirement. The pressing process is performed at room temperature with the required pressure varying from 1,380 MPa to 2,760 MPa [200 to 400 X 103 psi] depending on both the hobbing metals and blanking material. The pressing capacity of large scale hobbing machines may run as high as 2,722 tonnes [3,000 tons]. For the average production hob the pressure needed is much lower. HDT utilizes a 181 tonnes [200 tons] hydraulic press. This is more than sufficient pressure for most any production project. A retaining ring is used to prevent shape deviation or mold spreading.
Master hobs can be used repeatedly and may supply an unlimited number of impressions with great fidelity in size and finish to the hob. The process of pressing the hob into the blank is known as coining. Cold-form hobbing is generally done with steel in a fully annealed state. In order to avoid heat distortion, a cavity in the steel is often the best choice for cold-forming blanks. In some cases, vacuum heat treating is done to minimize the need for polishing after heat treatment. This process allows for quick, cost-effective part production.
Cold hobbing makes very efficient use of material while producing very strong parts, as the material flows into the desired shapes, maintaining its grain structure. Traditional machining partially removes grain structure by cutting through portions of the workpiece, truncating sections of the grain and creating vulnerability along all spliced segments.
The cost-effectiveness of cold hobbing is apparent in high volume runs. This is because the set up time for cold forming products can be costly, however the time saved when producing a large quantity of parts makes the set up cost well worth it.
HDT uses M42 for machining master hobs. There are many benefits to this material when it comes to creating hobs, such as superior red-hardness, resistance to chipping and abrasion resistance to name a few. Rigidity and extremely low failure ratio means shorter cycle time in production runs and in turn, faster delivery times. Once the master hob is created, hob blanks can be manufactured from a variety of materials including M42, S7, S1, D2, M2, CPM V and CRUWEAR.
HDT cold hobbing experts have over 50 years combined experience and are among the top technicians in the industry. If you have questions, they have answers. Call today to find out if cold hobbing is the smart choice for your next project.