Injection molding machine having a platen for uniform distribution of clamping forces

Abstract

An injection molding machine includes a movable platen specifically adapted to uniformly distribute a clamp force to the mold half surfaces thereby reducing localized deflections and unwanted flash on the molded article.

Description

first and second stationary platens platen 34a and clamp block 34b respectively.

A first mold half 26a is removably attached to a front face 12 of the movable platen 10. A second mold half 26b is removably mounted to second stationary platen clamp block 34b such that mold halves 26a and 26b form a mold cavity 28 therein when brought into contact during clamp-up by clamp column 20. Attached to the first stationary platen 34a and in communication with mold cavity 28 is an injection unit 36 which selectively provides molten resin to mold cavity 28 under high pressure and temperature for the formation of an injection molded article. As the high pressure resin enters the mold cavity, the pressure acts to separate the two faces of mold halves 26a and 26b. It is this injection pressure that the clamping force generated by clamp column 20 must resist.

A plurality of structural ribs 18 extend from back face 14 to front face 12 and provide the means for uniformly distributing the clamping force across the face of mold halves 26a and 26b.

Referring now to FIGS. 2, 3a, 3b and 4, a more detailed view of platen 10 in accordance with the present invention is shown. A plurality of back faces 14a-14d all separated by a center void 22 interface with singular clamp column 20 for the application of a clamp force Fc. The center void 22 creates four separate but coplanar surfaces for the application of the clamp force. Substantially parallel to and displaced from back faces 14a-14d is front face 12 which is specifically adapted to removably attach a mold half 26a. A top wall 46, bottom wall 48 and webs 42a and 42b extend rearward from the periphery of front face 12.

A plurality of ribs 18 extend from rear faces 14a-14d and attach to the back of front face 12 and top wall 46, bottom wall 48 and webs 42a and 42b. Each rib 18 is similarly shaped, exhibiting a trapezoidal shape extending from the back faces 14a-14d to front face 12, top wall 46, bottom wall 48 and webs 42a and 42b. The location, size and pattern of the ribs 18 in combination with the other structural elements, creates a uniformly supported and rigid front face 12. In the preferred embodiment, the location and size of the plurality of ribs 18 are based on structural analysis which yielded an optimized structural design. The optimized structural design defines a structure that uniformly transmits the force from the center clamp column 20 to the front face 12 and minimizes uneven deflections that may occur during clamp-up. Additionally, the optimized structure has resulted in a lower overall weight for the movable platen 10 and this reduces the energy requirements to open and close the mold and allows for quicker cycle times.

The preferred embodiment of the present invention is made from a cast shape of cast iron. It could however easily be made from a casting, weldment or built from separate structural components of suitable material all tied to together in a suitable fashion.

In the prior art, due to uneven sealing pressures that would be substantially lower at the outside edges of the mold as compared to the point where the clamp column 20 is applied, clamp tonnage was oversized to ensure adequate sealing along the outside edges of the mold. In accordance with the present invention, sealing pressures are substantially uniform across the face of the mold, and therefore do not require the clamp tonnage to be oversized. This results in the use of smaller and more efficient injection machine components and a reduction in the energy required during the molding process.

Provided at the bottom two corners of platen 10 are guide blocks 24a and 24b which interface with rail 40. Rail 40 guides the platen 10 in a back and forth direction when the mold is being opened and closed.

Attached between a pair of ribs 18 at the top and bottom of movable platen 10 are stiffeners 44a and 44b respectively. In the preferred embodiment, these stiffeners are t-shaped T-shaped stiffeners adapted to increase the structural rigidity of movable platen 10 and increase the load transmission capabilities of ribs 18. Attached to a pair of ribs 18 located at the inside and outside of movable platen 10 is a pair of vertical members 50a and 50b. In the preferred embodiment, these members are singular webs that tie together ribs 18 in those specific locations to increase the load transmission capabilities of movable platen 10. Location and size of vertical members 50a and 50b are based on structural analysis that yields an optimized design.

Referring specifically to FIG. 2, it can be seen that the present invention provides an optimized movable platen 10 structure for the uniform transmission of a clamp force Fc to mold half surfaces. As a result, a uniform pressure distribution P exists at the mold half surface and localized bending and deflections are minimized. The primary advantage to this arrangement is the reduction of clamp force while still avoiding flash on the molded article.

Another advantage of the present invention is that an injection molding machine having a lightweight platen is provided. This allows for the use of less power to move the platen and allows the platen to be moved quicker thereby reducing cycle times.

Still yet another advantage of the present invention is the reduction in energy usage of the molding machine to hold a mold closed during a molding operation due to a uniformly distributed sealing pressure.

It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.

Claims

1. A mold support platen adapted to be slidably carried on at least one of an injection molding machine, said platen comprising:

a substantially rectangular front face specifically adapted to carry a mold half;

a back face parallel to and spaced from said front face specifically adapted to interface with at least one clamp column, said clamp column configured to produce a clamping clamp force substantially in the center of said back face and applying a force substantially perpendicular to said front face;

a wall having a predetermined thickness and height protruding extending rearward from the periphery of said front face;

a plurality of spaced apart ribs extending in a predetermined pattern between and interconnecting each of said back face, said wall and said front face, wherein said force from said clamp clamp force applied by said clamp column is substantially uniformly transmitted from said back face to said front face thereby creating a uniform sealing pressure distribution during clamp-up.

2. The mold support platen of claim 1, wherein said back face further comprises a center void located in the center of said back face thereby creating four separate coplanar faces for the application of said clamp force.

3. The mold support platen of claim 1, further including clearance for the passing of a plurality tie-bars the length of said injection molding machine, said plurality of tie-bars not supporting said platen.

4. The mold support platen of claim 1, further comprising a first and second stiffener, each said stiffener attached at a predetermined location between and connecting a pair of said ribs located at the top and bottom of said platen.

5. The mold support platen of claim 4, wherein said first and second stiffeners are substantially t-shaped T-shaped and further attach to said wall.

6. The mold support platen of claim 1, further comprising a first and second vertical member, each said vertical member attached at a predetermined position between and connecting a pair of said ribs located at the inside and outside of said platen.

7. The mold support platen of claim 1, further comprising at least one guide block in movable communication with said at least one rail.

8. The mold support platen of claim 7, further comprising at least one web attached to and connecting said wall to said at least one guide block.

9. The mold support platen of claim 1, including a mold adjacent said front face.

10. The mold support platen of claim 9, including an injection unit connected to said mold.

11. The mold support platen of claim 10, including a means for generating a mold clamping force adjacent said front face.

12. The mold support platen of claim 1, wherein said plurality of ribs forms a symmetrical pattern.

13. The mold support platen of claim 1, wherein each said plurality of ribs is substantially trapezoidal.