1. The Field of the Invention
The invention relates to a method and an arrangement for gaging (also referred to herein as “gauging”) a thread produced in at least two working steps.
2. Background and Relevant Art
For thread production or thread rework, exclusively cutting, exclusively chipless and both cutting and chipless methods and threading tools are known.
Coming within the scope of cutting threading tools are taps (cf. Handbuch der Gewindetechnik und Frästechnik [Manual of threading practice and milling practice], publisher: EMUGE-FRANKEN, publishing firm: Publicis Corporate Publishing, year of publication: 2004 (ISBN 3-89578-232-7), designated below only as “EMUGE manual,” chapter 8, pages 181 to 298) and thread milling cutters (cf. EMUGE manual, chapter 10, pages 325 to 372).
Coming within the scope of chipless thread tools are “thread formers” (cf. EMUGE manual, chapter 9, pages 299 to 324) and “circular thread formers” (cf. WO 02/094491 A1 or DE 103 18 203 A1). An advantage of the chipless thread production compared with the cutting thread production is that, due to the consolidation or compaction at the surface, the hardness of the material in the region of the thread profile increases and thus a more wear-resistant thread can be produced.
Finally, combined methods having at least two working steps for producing internal threads are known, in which, in a first working step, a preliminary thread is produced and, in a further working step, the internal thread is completed by forming from the preliminary thread. Due to this two- or multi-stage method, the entire volume of the thread profile does not have to be produced by a single forming tool by plastic deformation of the material, and the loading and the wear of the forming tool are reduced.
For such a combined method having a plurality of working steps, a separate tool can be used in a first variant in each working step. DE 10 2004 033 772 A1 discloses such a method, in which, in a first working step, a preliminary thread is initially produced in the workpiece with a cutting or chipless action by means of a tap, thread milling cutter, by turning, grinding or winding or also by means of a thread former and, in a second working step, the finish production of the preliminary thread is effected with a chipless action using a thread former or circular former, the forming wedges of which press into the thread root of the preliminary thread. The forming wedges are in this case centered by widened portions of their flanks in the initially produced thread.
The thread flanks of the preliminary thread produced in the first working step remain unchanged in the second working step, since the widened portions of the forming wedge flanks bear only against the preliminary thread flanks for centering, but do not deform the latter. In the second working step, the workpiece material is deformed further only in the region of the thread root, connecting the two thread flanks, of the preliminary thread. As a result, in the second working step, the entire thread root and also those regions of the thread flanks of the final thread which directly adjoin the thread root and lie in extension of the thread flanks of the preliminary thread are completed by forming and are thus additionally compacted and consolidated, whereas the predominant region of the thread flanks of the final thread have already been completely produced in the first working step and have not been worked further in the second working step.
In a second known variant of a combined method having a plurality of working steps, a combination tool having a cutting tapping part and a chipless thread-forming part, offset axially to the tool axis relative to the tapping part, on a tool shank is used, the tapping part, with rotation about the tool axis and with axial feed, cutting a preliminary thread in the workpiece in a first working step, and the following thread-forming part forming the preliminary thread in a predetermined manner in a second working step in order to produce the final thread. The tap therefore initially cuts the thread and the thread former subsequently partly forms the initially cut thread. Such an axial combination tool and method are known from DE 70 17 590 U and DE 196 49 190 C2.
According to DE 196 49 190 C2, the thread is first of all produced with a precise profile and accurately to size in the thread flanks by a cutting action by means of the tap of the combination tool and then only the thread root of this initially cut thread is compacted with a chipless action to a predetermined final diameter by the directly following thread former. As a result, in particular the first thread turns, following an initial thread cut, can be produced in such a way that they are more resistant to vibrations and are less susceptible to fracture. In the second working step, the two thread flanks cut by the tap in the first working step remain completely unchanged.
DE 70 17 590 U1 discloses a combination tool for producing internal threads, having a tapping drill, designed as a taper or second tap, as a front tool part for the initial cutting of the thread and a thread former, adjoining in the working direction, as a rear tool part for the finishing of the thread.
General terms and sizes and also parameters of threads and various thread types are standardized nationally and internationally, e.g., in DIN 2244, and are obtained from the EMUGE manual, chapter 15, pages 468 to 566.
The simple flank diameter of the internal thread is the diameter of the geometrically ideal circular cylinder, the generating lines of which intersect the thread in such a way that the sections in the thread gaps are equal to half the pitch. The axis of the circular cylinder is coaxial to the axis of the flank diameter.
The flank diameter of an external thread or internal thread is the diameter of a geometrically ideal circular cylinder, the generating lines of which intersect the thread Min such a way that the sections of the generating line which are formed by a thread gap and an adjacent thread tooth of the same are equally long. The axis of the circular cylinder is again coaxial to the axis of the flank diameter.
EMUGE manual, in chapter 12, pages 405 to 422, gives an overview of thread gages for gaging or testing threads.
A thread go plug gage and a thread no-go plug gage are used for gaging or testing an internal thread, in particular a nut internal thread.
The thread go plug gage tests the “pairing dimension” of the internal thread and the screw-in capacity. In this case, the smallest dimension of the internal thread flank diameter including certain errors of form in the thread, e.g., pitch deviations and thread profile angle deviations, and the smallest dimension of the outside diameter of the internal thread are tested. It is thus tested whether the straight thread flank piece is sufficiently long. The minor diameter of the internal thread is not tested. It must be possible to screw in the thread go plug gage manually over the entire length of the workpiece thread without applying special force.
The thread no-go plug gage tests whether the actual flank diameter of the internal thread exceeds the prescribed maximum size. The internal thread outside diameter and the internal thread minor diameter are not tested. The thread no-go plug gage may be screwed into the workpiece from both sides by not more than two revolutions without applying special force and therefore generally has a thread length of at least three thread turns. The thread profile generally has shortened thread flanks.
The thread limit plug gage is the combination of thread go plug gage and thread no-go plug gage on one handle.
The internal thread minor diameter is tested using a smooth, cylindrical go and no-go plug gage or limit plug gage. In principle, the internal thread minor diameter should be tested before gaging the internal thread flank diameter. The smooth go plug gage must be capable of being passed through the workpiece thread manually without applying special force. The thread on the gage plugs or gages is adapted to the thread to be measured, in particular to an ISO metric thread or a tapered thread or a self-locking thread.
The gaging or testing of produced threads is carried out at the end of the thread production or on finished threads.