Posted at 11.03.2018

Content

- 1. Introduction
- 2. Broaching tool geometry
- 3. Mechanics of metal slicing in broaching
- 4. Cutting edge interpolation by B-spline parametric curves

- 5. Computation of chip weight and contact length
- 6. Cutting forces simulation
- 7. Results and discussion
- 8. Conclusion
- Acknowledgment
- The authors acknowledge the Natural Sciences and Executive Research Council of Canada (NSERC) for his or her support to the project.

According to variety of workpiece profiles in broaching, the geometry of cutting edge varies from simple lines to very complicated curves. Wide range of leading edge geometry in broaching imposes complexness to the distribution of the chip insert along the cutting edge. Hence, prediction of lowering makes in broaching is not as simple as other machining processes. Because of this complexity, producing an applicable push model for all the orthogonal and oblique broaching cutters can be problematic. In this newspaper, an attempt was created to present a new make model for broaching. The recently proposed power model expresses the leading edge as a B-spline parametric curve and uses their versatility to analyze the chip weight as well as trimming pushes for orthogonal and oblique broaching. Verified by experimental results, the presented model has a great capacity to simulate broaching cutter geometry along with chopping forces and it can be applied for the entire broaching cutters.

Broaching is a robust process for the production of complex interior and external information. Like a machining process, it is commonly used for the machining of a wide range of information such as keyways, guide ways, openings and fir-tree slots on turbine discs. Broaching has appreciable advantages compared to other machining processes. Roughing, semi finishing and finishing of any complex profiles can be done in one stroke of the machine which would require many moves in other traditional processes such as turning, milling, slot milling, etc. Additionally, it may produce parts with high surface quality and high geometrical and dimensional tolerances in a single stroke. Since the number of all together engaged cutting sides with the workpiece is higher than the other reducing tools, the chip weight on all of them will be smaller and tool life is distinctively longer in comparison to other machining functions such as milling and turning [1]. It could be also pointed out that broaching machines aren't as complicated as CNC milling or CNC turning machines and so considered as a straightforward operation that requires not a very skilled operator. In other frequently used machining operations such as milling and turning, last geometry of workpiece is produced by combination of tool and workpiece movement and there is absolutely no similarity between final geometry of workpiece and reducing tool geometry. In broaching, the geometry of machined part comes from straight by the inversion of broaching cutter geometry. Therefore unlike other machining operations, broaching cutters have a wide range of geometries as well as parts. As a result, chip fill has a complicated non-uniform 2D or 3D geometry depending on the profile complexity of workpiece. A unique feature of broaching operation is that it is not possible to improve the cutting parameters during process but the cutting speed. That's because all other cutting guidelines such as feed, depth of chop and width of cut are designed in top features of broaching tool geometry which makes the tool design the most crucial aspect of broaching.

Although broaching is well identified in industry, just a limited quantity of researches have reported work on view literatures. In 1960 Monday [2] reveals the most detailed source on broaching. An in depth information of broaching technology can be found in his publication. Kokmeyer [3] edited assortment of works on broaching representing the effectiveness of the procedure. Gilormini et al. [4] examined the cutting forces about the same broaching and compared these to the forces in slotting and tapping process. Terry et al. [1] shown a system for maximum design of broaching tools. They shown the factors that affect efficiency in broaching and described the design constraints, their importance and exactly how they are picked. Finite aspect was used to anticipate the tooth deflection and experimental data to be able to create the overall rules for creating. Sutherland et al. [5] presented a drive model for broaching predicated on the oblique analysis to determine the forces in the gear broaching process. Their model exhibited the relationship between contact area, chip fill and cutting pressure. Sajeev et al. [6, 7] looked into the consequences of broaching guidelines on the tool and workpiece deflections and the ultimate condition of the broached geometry. Budak [8] reviewed the performance of broaching tools used for broaching of waspaloy turbine discs with fir-tree account based on the monitoring of power and power. It has been shown that for the majority of the investigated tools, the strain distribution one of the broaching parts were non-uniform resulting in uneven wear. Recently Ozturk and Budak [9, 10] performed Finite Element Analysis to estimate the stresses in the broaching tool during the cutting process. The developed model is used to simulate the broaching process and anticipate the generated stresses in the tool to improve the tool design. He examined fir-tree information, simulated the broaching process forces and the tool tensions to improve the tool design. Later Kokturk and Budak [11, 12] performed an optimization on the geometry of the broaching tool lowering edges. In their study the slicing conditions are improved until they can satisfy the preset constraint. In addition they used the optimized conditions to improve the broaching process. Yussefian et al. [13] applied B-Spline parametric curves in modeling of monotonous process. Lately Hosseini and Kishawy [14] presented a general force model for orthogonal broaching using B-spline interpolation of cutting edge. By firmly taking geometric flexibility of B-spline curves, their model was capable of modeling any arbitrary orthogonal broaching leading edge geometry as well as processing the chip insert for various slicing conditions. This paper proposes a 3D basic make model for the broaching process. The proposed power model is with the capacity of modelling of three force components using B-Spline interpolation of the cutting edge. Each leading edge is first modeled by B-Spline parametric curves then the chip fill is calculated by integration of area between two successive edges. The proposed make model for orthogonal and oblique broaching can analyze the chip fill for any arbitrary geometry of cutting edge from the easiest to the most complicated. The proposed method is used to calculate the generated causes and the results are set alongside the measured data.

Broaching tool is a right multi tooth cutter where several cutting ends build relationships the workpiece together and each teeth removes a portion of material from workpiece surface. Broaching cutter has a tapered toned or round profile with some teeth on its surface [4]. Each successive tooth in a broaching tool is higher than the preceding someone to perform the cutting action and remove materials from workpiece surface. Broaching cutters in their general form can be geometrically divided into three types of teeth, specifically, roughing, semi-finishing and completing teeth. Roughing pearly whites remove the bulk of material from workpiece, semi finishing teeth produce the basic surface surface finish (surface quality), and completing teeth provide the last surface finish and established geometrical and dimensional tolerances [4]. Number (1) shows an average broaching reducing tool.

Figure 1: Schematic view of broaching tool

Normally the maximum rise per tooth in broaching tool belongs to the roughing tooth which perform the major part of material removal. The rate of growing per tooth somewhat reduces in semi finishing tooth as they only remove a tiny portion of material from workpiece surface to increase the dimensional precision and surface quality. Within the finishing part, every one of the pearly whites have the same level. These teeth aren't cutting teeth plus they supply the desired surface quality and adapt the geometrical and dimensional tolerances in the predefined range. Amount (2) illustrates the general mechanism of slicing in broaching.

Figure 2: System of lowering in broaching

When broaching cutter is effectively designed, broaching process can be faster and even more accurate than a great many other machining techniques. Although the original cost of establishing for a broaching process is comparatively greater than that of other chopping processes, the development cost is commonly low due to high creation rates and the long tool life. Number (3) presents some of the top geometrical guidelines of broaching lowering tool.

Figure 3: Broaching tool geometry

In physique (3), and are rake angle, clearance (comfort) angle, teeth level and land period respectively. The rake viewpoint and clearance perspective can be chosen predicated on workpiece material. The rake perspective is usually decided on between to and clearance angle is usually picked between to [12]. The full total amount of the tool and number of simultaneously engaged trimming ends can be determined by the pitch period which is a linear distance between two successive cutting edges. Predicated on some previously conducted research [10, 12, 15], it is figured it surpasses have at least two reducing edges in trim to have a dynamically stable trimming.

Another geometric feature of broaching tool is gullet space which is the bare space between two following teeth. The main good thing about gullet space is to retain the chip during cutting until the teeth leaves the workpiece. After the broaching tool engages with the workpiece, chip is captured between tool and workpiece and it is looked after there until each teeth finishes the cut and leaves the workpiece. Small gullet space may cause tool breakage because of no space to keep carefully the removed chip. It can also lead to poor surface finish off anticipated to rubbing of removed chip to the machined surface. In the event the gullet space is chosen too large it makes the tool very slim and decreases the tool power and stability. Based on the previously listed reasons, it is vital to create the gullet space effectively to achieve appropriate space and active stability simultaneously. In order to perform an acceptable design it's important to have a good knowledge of cutting forces during machining process. If the push model can predict the cutting pressure truthfully the result of power simulation can be utilized as an type for design and search engine optimization process.

Similar to almost all of the cutting procedures, the cutting push in broaching can be indicated generally by three differential components that are directly related to chip weight area and the contact period between leading edge and workpiece in a way that [16]:

(1)

Figure (4) depicts the key features of oblique broaching and shows the make components generated through the chip removal process.

Figure 4: Technicians of oblique broaching

In equations (1), is the differential element of tangential pressure, is the differential element of feed force and is the differential element of radial force. and are chip thickness and amount of the cut for infinitesimal aspect along the leading edge respectively. and are trimming and edge constants as the subscript refer to the tangential, feed and radial directions. Like the other cutting mechanics, the radial element of force shows up only during oblique broaching when leading edge comes with an inclination angle with the trimming direction. The total tangential, give food to and radial element of cutting force for every single advantage can be computed by integrating of these components over the cutting edge. Equation (2) shows the push integration along the cutting edge from the begin to the end of engagement.

(2)

In formula (2), symbolizes a differential element of chip area which is removed by the leading edge. Equation (2) can be written in this format:

(3)

In the above formula, is chip weight along the leading edge and is amount of engagement between cutting edge and workpiece. Shape (5) shows the infinitesimal factor of leading edge, chip fill and contact duration for an arbitrary fir tree broaching tool.

Figure 5: Infinitesimal component of chopping edge

Since the chip load may vary across the broaching edge, it must be segmented into elements for which local thickness can be assumed constant. The geometry of chip along the broaching leading edge is complicated however, since there is absolutely no relative motion between successive ends the chip insert remains constant. The normal procedure for simulation of slicing makes is dividing the leading edge to infinitesimal elements and calculating the area for every single element separately. If total chip area can be calculated, cutting makes are obtained without the need for dividing the border to elements. However, due to the variety and the difficulty of cutting edge information in broaching, it is difficult expressing the advantage by an explicit function. Hence, computation of the aforementioned integration in formula (3) is not a straight forward process. Representing the broaching leading edge by B-Spline curves is a powerful way to express the geometry with parametric relationships which makes integration and derivation across the edge easier process.

A group of data point can be acquired by collecting the coordinates for every point across the leading edge using inspection method such as CMM, digitizing or laser beam scanning. The required B-Spline of level p identified by control factors passes through those data factors and expresses the leading edge with a parametric curve. This parametric representation of the leading edge can be easily appllied to perform derivation and integration across the edge to get the chip weight area and the full total engagement size. The interpolated B-spline cutting edge of degree p can be expressed as below [17-19]:

(4)

Where is interpolating B-Spline curve of degree p, is control factors which control the geometry of curve and it is B-spline Basis functions that can be computed by:

(5)

In formula (5), is a B-spline knot which is one of the knot vector of. The formula (4) has mysterious control points. Because of this, it's important to have a parameter prefer to relate the control things to the info details. Since parameter corresponds to data point, plugging into the above equation produces the following [19]:

(6)

There are n+1 B-spline basis functions and parameters in equation (6). Substituting t directly into, these values can be planned in a matrix N as shown as below:

(7)

Data factors and control details can be indicated in similar way:

(8)

And

(9)

In formula (9) matrix D is type data points that are represents the factors along the leading edge and matrix N can be acquired by analyzing B-spline basis functions at the given parameters [19]. D and N both are known and the only real unfamiliar parameter is matrix P. Equation (9) is a system of linear equations with unknown P, handling for P yields the control tips and the required B-spline interpolation curve becomes available. Shape (6) shows control things and desired interpolated broaching cutting edge using B-spline curves.

Figure 6: B-spline interpolation of trimming edge

In orthogonal broaching, every one of the cutting ends are parallel alongside one another and perpendicular to the cutter axis therefore the third column of matrixes and in equation (8) are zero in support of two guidelines of and in equation (4) is required to represent the cutting edge. Numbers (7a) and (7b) depicts a typical Cartesian coordinates in orthogonal and oblique broaching.

(a) Orthogonal broaching

(b) Oblique broaching

Figure 7: Cartesian coordinates

In distinction with orthogonal broaching where all tooth are perpendicular to the cutter axis, in oblique broaching cutting edges produce an oblique position with cutter axis nevertheless they are still parallel to each other. In cases like this, , and all of the coordinates in the third column of matrixes and are non zero. B-spline interpolation of 3D curves can be done but tiny bit time consuming so it is preferable to change the 3D to 2D and use the same method for 3D after change. Coordinates of point in Cartesian coordinates can be portrayed by in plane as follows:

(10)

The above transformation can be done for most of cutting edge data items and in the new coordinate system matrixes is really as follows:

(11)

Once matrix offered in new coordinate system the interpolation process can be carried out exactly like previous method for 2D curves. When the leading edge is shown by B-Spline curves, chip area and reducing length for every single leading edge can be calculated immediately from B-Spline equations as follows [13]:

(12)

Where indicate start of the trim, end of the chop, current cutting edge and previous leading edge respectively. Formula (12) has two coordinate parameters and it is applicable for calculation of chip insert and contact length for orthogonal and oblique broaching.

In order to compare the presented geometric model with a genuine circumstance, a broach cutter was determined and its lowering ends were modeled using B-Spline curves. The geometry of cutter was chosen based on previously offered research by Kokturk [12] to validate the newly proposed model capability. Figure (8) demonstrates the cutter geometry.

Figure 8: Cutter geometry

The geometrical features of cutting edge are available in stand (1) [12].

Table 1: Geometry of broaching cutter [12]

In the next step, selected cutting sides were interpolated using suggested approach. Similar to other interpolation methods, B-Spline interpolation is hypersensitive to the number of data tips. Increasing the number of data points produces a better accuracy and reliability but it makes the operating time of the algorithm much longer. Decreasing the amount of data points, accelerate the algorithm but it has a negative effect on the accuracy. It's been shown that soft elements of the curve aren't very delicate to the amount of data details because inaccuracy occurs in the razor-sharp corners where the curve course changes suddenly. Because of this, it would be better to use more data things at the razor-sharp sides and less data point at the other areas to improve the accuracy and reliability and time efficiency of the algorithm together. Characters (9a) and (9b) show the B-Spline display of two successive trimming edges.

(a) B-spline representation of the first trimming edge

(b) B-spline representation of the second cutting edge

Figure 9: B-spline representation of two successive lowering edges

It can be seen from the above statistics that B-Spline curve uses the info point at the sharp spot with high correctness.

Figure (10) shows the final geometry of workpiece. Reducing conditions and pressure coefficients which are used in simulation can be found in table (2).

Figure 10: Last workpiece geometry

Table 2: Chopping conditions [12]

5

Since the cutting edge without oblique angle doesnt have radial component of cutting power it was assumed that because of this special circumstance. The border coefficients of lowering power are always very small compared to cutting coefficients so it has been assumed that, and are negligible.

Figure 11: Simulated and experimental lowering forces for orthogonal broaching

Figure 12: Simulated and experimental resultant drive for orthogonal broaching

Figure 13: Simulated and experimental lowering causes for oblique broaching

Figure 14: Simulated and experimental resultant push for oblique broaching

It is seen from figures (11) to (14) that the results of newly proposed model are in good arrangement with the previously publicized results [12]. Since there is no oblique viewpoint in orthogonal broaching the cutting edge engaged with workpiece all of the sudden with full length so there is a jump in force diagram when each teeth engaged with workpiece. Because of occurrence of oblique perspective in oblique broaching the teeth employed with workpiece well so the cutting forces rise steadily from zero to its last value. Also, in oblique broaching, fluctuation of trimming makes in the constant state part of the cutting is significantly less than orthogonal one since when one of the teeth leaving the workpiece another one engages smoothly however the average force is higher because of longer contact period.

In this newspaper, a drive model is developed to simulate the trimming forces in orthogonal and oblique broaching using B-spline representation of the leading edge. The brand new model can interpolate broaching tool cutting edge without any constraints which offer the simulation of lowering forces for any desired suggestions geometry. To be able to validate the new power model, the predicted reducing forces are compared to previously measured data [12]. The comparability showed a good agreement in both assessed and predicted data for orthogonal and oblique broaching. The simulated lowering forces can be used to have a better knowledge of process and improve the geometric features of broaching cutter to attain more efficient cutting which is under research of creators.

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