GB2115735A - Press knife - Google Patents

Abstract

A press knife and method of constructing same, according to which the press knife consists of metal strip material (18, 20) formed with one or more bends roughly corresponding to a desired configuration of press knife, and a support plate shaped accurately to correspond with the desired configuration, the metal strip material being conformed to the accurately shaped support plate and fixed thereto in said conformed position. In the case of a press-knife for cutting leather, the support plate may have prickers 28 mounted thereto. In a preferred method, data for controlling the forming of the support plate into its accurate shape is generated by a computer. <IMAGE>

Description

SPECIFICATION Cutting tool construction Field of Invention This invention concerns the construction of cutting tools, particularly tools for cutting out areas of sheet material such as leather as a preliminary stage to a manufacturing process.

The invention is of particular application to the construction of press knives for cutting out leather blanks from which boots and shoes can subsequently be constructed although it is to be understood that the invention is not limited to this particular type of cutting tool.

Background to the Invention Shoe manufacturers currently manufacture press knives for leather cutting by a manual method using card templates. Variation of style, width and size mean that only one knife of each type is usually required and fashion changes demand a regular flow of new profiles.

One present method of manufacturing press knives employs a V-block into which the blade is bent locally under the action of a foot-operated pin or other deflecting device. The operator uses a card template as a visual guide and by creating a number of bends at discrete points along the. blade produces a profile which approximates adequately to the desired smooth shape of the card blank.

Where particularly acute bends are required, a combination of heat and broaching, together with additional tools enables the operator to produce the substantial deformation without cracking the material.

The blade has to be bent through a greater angle than is actually required in order to allow for springback in the material and the degree of overbending is achieved through experience and skill of the operator and the continuous visual inspection which he provides.

A profile tolerance achievable with this method of construction is typically plus or minus 1/64" (+ on -0.4 mm) and a knife for a piece such as an in quarter will require approximately 60 discreet bends.

Our co-pending Application No.

entitled "Method and apparatus for designing and making cutting tools" describes an improved method of constructing a press knife for cutting out sheet materials such as leather and further describes apparatus for performing the improved method.

The aforementioned method involves inter alia the step of incrementally advancing strip material through a bending station and introducing bends in the strip material under the direction of machine instructions so as to form a blade from the shaped strip material.

The aforementioned method has to be performed to a high level of accuracy since any small error in each of the bends will tend to be cumulative and the result will be that the two ends of a blade or the two or more sections of a multiple-part blade constructed in accordance with the aforementioned method will not necessarily join up correctly unless exactly the right angular bends are introduced into the material.

The present invention provides an improved construction of press knife which does not require the bending of the strip material to be performed to such a high degree of accuracy.

Summary of the Invention According to the present invention an improved press knife for cutting out sheet materials such as leather comprises: 1) a length of strip material containing at least one bend and forming either the whole or a part of the knife blade of a press knife; 2) a solid plate shaped to conform to the desired shape of the blade of the knife and dimensioned so as to correspond to the internal peripheral shape of the desired form of knife blade, the blade portion or portions being secured to the solid plate member by brazing or welding or other securing means; and 3) a plurality of pinholes in the solid plate through which pins or so-called prickers are inserted and secured.

The solid plate which constitutes a web within the knife may be formed with a one or more larye apertures to allow removal of the cut sheet material from the knife when in use. Such apertures may also serve as locations datums for manufacture.

The solid plate member is preferably cut using laser cutting, flame cutting, plasma cutting, NC nibbling or profile milling.

According to a preferred method of manufacture, the solid plate is first of all cut out to a high standard of accuracy using information stored in a computer memory corresponding to the desired profile shape and dimensions. The accurate solid plate so formed constitutes a template around which formed metal strip can be located and accurately positioned before it is welded, brazed or otherwise secured to the plate.

The bending of the strip to form the blade or segments which, when secured in edge juxtaposition, constitute the blade, may be formed by any convenient bending method including manual bending or incremental bending in the manner described in our aforementioned co-pending Application.

According to a preferred feature of the invention, the information used to form the plate may itself be used to assist in the bending of the strip to form the blade or blade segments.

According to a further preferred feature of the invention, the shape of the sheet material blank which is to be cut out using the knife is itself determined using a computer and visual display unit (VDU) having so-called computergraphics capability and information relating to the size and shape of the outline required for the final blade is stored in a memory associated with the computer and this information is employed to cut out the support plate and may be used to control a bending operation to form the blade or segments of the blade from the strip material.

Preferably means is provided for marking the solid plates automatically as they are cut out or stamped out or otherwise formed so that each bears an appropriate code which can then be related to a similar code or complementary code added to each of the blade sections or a blade which is to be fitted around the plate. In this way the correct blade or blade sections can be selected to fit around the plate.

According to a further preferred feature of the invention, information relating to the complete range of different sizes of solid plates which are required to form a set of knives which can then be used to cut out the different blanks required for a complete range of sizes of garment or shoe or boot is contained within a computer memory or is computed from information relating to a midrange size of blank for that particular garment or shoe or boot and the appropriate profile and dimensional information is selected for the formation of each solid plate and the subsequent bending of strip material so as to form the component parts which when joined together form a knife suitable for removing sheet material to the precise shape and size required to form any particular blank.

The invention also lies in an accurately cut and accurately dimensioned and shaped solid plate member which can be used as a template by which other similar solid plate blanks can be cut or otherwise formed so as to form a complete range of press knives for removing areas of sheet material and, further, to provide a template or guide by which a length of strip material or lengths of strip material can be bent or otherwise formed into the blade shape for fitting around each of the solid plate webs.

It will be seen that once the accurately shaped solid plate has been cut out or otherwise formed, the bending of the strip material to form the peripheral blade for the plate can be performed to a much lower level of accuracy than is required if the bending of the strip is itself to dictate the peripheral shape of the knife and the invention allows the more accurate process of cutting, particularly using laser cutting or the like to produce accurately the size and shape of the cutter blade which thus takes away the need to form the bends in the strip material from which the blade or blade sections are to be formed to such a high degree of accuracy as would otherwise be the case if the central solid plate is not the shape determining factor in the construction of the overall knife.

In a method of forming a knife from a shaped solid plate member, the latter is used to control a bending machine or is used as a template around which strip material is bent manually so as to form a shaped blade or two or more independent blade sections which can subsequently be fitted around the periphery of the solid plate member and secured thereto by way of brazing or welding or the like and may be secured the one to the other at their juxtaposed ends again as by welding or brazing or the like.

In a method in which the shaped solid plate member is used as a template for controlling a bending machine so as to produce a shaped and appropriate dimensioned blade or blade section, the accurately cut out solid plate member may be inserted into a template reading station which includes at least one follower adapted to move around the periphery of the shaped solid plate member so as to generate from the movement therearound coordinate information or lengthened angular information or both which is used to dictate the operation of the bending machine so as to produce a complementary shaped blade or blade section.

The invention also lies in a press knife or the like when constructed by the method as described in our aforementioned co-pending Application or as described herein.

The invention allows an improved press knife to be constructed relative to the form of press knife known from present techniques and methods of manufacture in that the separate narrow fillets or strips which have hitherto been used to form the web within such knives are replaced by a single member which dictates the final shape of the blade and thus acts as a primary or secondary control on the final shape of the blade and therefore the accuracy with which the cutter is constructed.

Although the solid plate member has been described as being formed from metal (and this would be the normally preferred material) there is no reason for the shaped solid web to be formed from a plastics material or a laminate material or a combination of metal and plastics material or even from wood or wood and plastics.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a perspective view of a profiled solid plate member constructed in accordance with the invention; Figure 2 illustrates two blade segments adapted to be fitted around a plate member as shown in Figure 1: Figure 3 is an elevation of a pin or pricker adapted to be inserted in the plate of Figure 1; and Figure 4 is a perspective view of the fully assembled knife.

Detailed Description of Drawings In Figure 1 there is shown a profiled and accurately cut out or stamped plate generally designated 10 which constitutes the central rigid web of a knife for removing areas of sheet materials such as leather or fabric material for the purpose of forming blanks from which shoes, boots or clothes can be formed.

The blank is formed by an accurate cutting process such as laser cutting or NC nibbling or the like and includes one or more central apertures (two being shown in Figure 1 at 12 and 14) and a plurality of small holes such as 1 6.

The apertures such as 12 and 14 allow sheet material adhering to a blade and located within the blade profile to be pushed out when the knife is in use.

The smalier holes such as 1 6 are adapted to receive prickers or pins (to be described) which can be secured therein so as to protrude on at least one side if not both sides of the plate.

Figure 2 shows two segments 18 and 20 of a blade formed from strip material which is bent so as to conform to the outside shape and configuration of the support plate 10. The segments 18 and 20 are adapted to be welded or otherwise secured such as by brazing to the outside periphery of the plate 10 and the latter is used to constrain the blade segments 1 8 and 20 so as to form precisely the correct outline of blade.

The abutting ends of the two blade segments may themselves be welded or otherwise joined so as to form a continuous knife edge after the blade segments are fitted around and secured to the plate 10.

In Figure 3 there is shown to an enlarged scale a pricker. This comprises an upper pointed end 22 and a complementary lower pointed end 24 which are integral with a central generally cylindrical section 26 which may be grooved so as to form a good key with the material from which the plate 10 is formed when the cylindrical section 26 registers with the thickness of the plate 10.

The pricker is effectively a double-ended pin and the central generally cylindrical section 26 is dimensioned so as to correspond to the thickness of the plate 10 so that the sharpened pointed ends of the pin or pricker as it is called just protrude by the required amount from the opposite faces of the plate 1 0. The prickers may be secured in position as by an adhesive or bonding agent or may be simply push-fitted into position or may be welded or otherwise secured to the material from which the plate is constructed.

Figure 4 shows a completely assembied knife with prickers designated 28 fitted into the smaller holes 1 6 in the plate 10 and with the two blade segments 20 and 18 fitted around and secured as by welding to the external edge of the plate 10.

The plate 10 may be formed from metal or plastics material or wood or any suitable combination thereof.

Claims (15)

1. A press knife for cutting out sheet materials such as leather comprising: 1) a length of strip material containing at least one bend and forming either the whole or a part of the knife blade of a press knife; 2) a solid plate shaped to conform to the desired shape of the blade of the knife and dimensioned so as to correspond to the internal peripheral shape of the desired form of knife blade, the blade portion or portions being secured to the solid plate member by brazing or welding or other securing means.

2. A press knife as claimed in claim 1, wherein the solid plate has pin-holes in which prickers are inserted and secured.

3. A press knife as claimed in claim 1 or claim 2, formed with one or more large apertures to permit removal of sheet material from within the knife when the latter is in use.

4. A method of constructing a press knife for cutting out sheet materials such as leather comprising: - forming metal strip material with one or more bends related to a desired configuration of press knife corresponding to a particular profile of sheet material to be cut out, - forming a support plate with a shaped peripheral outline accurately corresponding to said particular profile, - assembling the formed strip material with the support plate to conform it to the shaped outline of the latter and fixing said strip material to the support plate in the conformed position in order to produce the press knife of the desired configuration.

5. A method according to claim 4, wherein the one or more bends in the strip material are formed in a bending machine which is controlled by information derived from one or more followers adapted to move around the periphery of the formed support plate.

6. A method according to claim 4, including the steps of generating data defining a required peripheral outline for the support plate, and utilising said data to control a forming device for said support plate.

7. A method according to claim 6, wherein the support plate is formed by laser cutting, flame cutting, plasma cutting, NC nibbling or profile milling.

8. A method according to claim 6 or claim 7, wherein machine instructions, derived from the said outline defining data, are fed to a bending machine which forms the one or more bends in the strip material.

9. A method according to any of claims 4 to 8, wherein the shape to be cut out of the sheet material by the press knife after construction of the latter is determined by use of a computer and VDU having computer-graphics capability, and the information relating to the size and shape of a particular desired configurated of press knife is stored in the computer memory and is extracted therefrom for controlling the formation of the support plate.

10. A method according to claim 9, wherein the computer memory is utilised to store a range of different shapes and sizes of press knife and means are provided for selecting a particular shape and size from the range in order to control formation of the support plate.

11. A method according to any of claims 4 to 8, wherein a computer is utilised to store information related to a basic size and shape of press knife and is programmed to compute from input information data corresponding to any one of a range of different shapes and sizes of press knife which may be required and to provide such computed data for the control of a forming device for the support plate.

11. A method according to any of claims 4 to 10, wherein the support plate is formed of metal and the formed strip material is secured thereto by welding or brazing.

12. A method according to any of claims 4 to 11, wherein the formed metal strip material is produced in two or more parts for assembly with the support plate.

1 3. A method according to any of claims 4 to 12, wherein the component parts of the press knife are marked prior to assembly with identification codes for ensuring matching of said parts.

14. A press knife substantially as hereinbefore described with reference to the accompanying drawings.

1 5. A method of constructing a press knife substantially as hereinbefore described.

1 6. A press knife constructed by the method of any of claims 4 to 13 or claim

1 5.